The main characters are Aelita Stones (later called by her birth name of Aelita Schaeffer), Jeremie Belpois, Odd Della Robbia, Ulrich Stern, Yumi Ishiyama, William Dunbar (later on), and XANA. The first five are the protagonists, commonly referred to as "the group" or "Lyoko warriors" in the series. They are the ones who attempt to foil XANA's plans. The sixth name mention can be considered either a protagonist or an antagonist. The primary antagonist is XANA, who seeks to take over the world.

Aelita Schaeffer-Hopper (Stones)

Aelita Stones (birth name: Aelita Schaeffer-Hopper) is the nearly youngest girl in the group and the most naive of the five, having had comparatively less experience with the real world than her friends. She is thought to be an A.I. within Lyoko at first. She is the daughter of Franz and Anthea Hopper, who designed both the supercomputer, Lyoko, and X.A.N.A. She manages to settle into her new life, making more jokes and generally displaying less naivety, and more reflected in her combat skills. Aelita is also capable of using the supercomputer in the event that Jeremie cannot. In the show it displays that she has feelings for Jeremie. On Earth, her full name is Aelita Stones. Later on, it is revealed that Aelita's true last name is Schaeffer, but that her father had changed it to Hopper, her mother's maiden name, to make a fresh start. Aelita's mother, Anthea Hopper, disappeared when she was young. It was mentioned that Anthea was kidnapped by the Men in Black when Aelita was a little girl and was never seen again. When Aelita was first materialized she was physically twelve, and her birthday remained unknown. She asked Jeremy to choose one for her. Aelita is around twelve to thirteen years old and in 8th grade, having been skipped ahead; Later on, she is still thirteen and in ninth grade.

Aelita's hair is bright pink and often thought to be dyed, but is in fact natural inherited from her mother, Anthea Hopper. She wears three main outfits. Her daytime outfit a first is a maroon skirt, yellow shirt and pink jacket. She wears a dark pink jumper dress over a light pink hooded long sleeved shirt and dark pink knee boots as a trademark outfit. But the non-trademark outfit, her outfit consists of a dark purple dress that comes to her knees and light pink Quarter length leggings underneath. Her boots are a deep red. Her night clothes consist of white socks (sometimes barefoot) and an over sized pink t-shirt with a red letter "A" on the front.

Aelita's Lyoko attire consists of a light pink-and-white mini skirt and a matching top that go over trousers and a long shirt that are both off-white, and matching shoes. She also has elf-like ears, with a small dangle earring in the left one. Her eyes are green. Later on, Aelita receives a new pink form-fitting suit on Lyoko, which has a pair of retractable energy wings that enable Aelita to fly. Also later on, Jeremie creates a program to send the Warriors to earth to destroy the replicas as polymorphic specter forms. Aelita's energized spectral form is a match to her original on Lyoko, except that her ears aren't pointed, her "Energy Fields" are yellowish-orange in color, and she has not used her wings.

Her main interest is music, specifically audio mixing. Her childhood memories show that Franz Hopper taught her to play the piano at an early age. Later on, she wins a contest to star in one of the Subdigitals' concerts. She, like Jeremie, is also a capable programmer and an excellent student. Aelita has four appearances on Lyoko. At first, she was a Lyoko being and wasn't allowed to be devirtualized and doesn't have any powers except for her "creativity." Later on, Aelita is a human being, but doesn't have any weapons. Later on, Aelita can conjure deep pink orbs from her hands called "Energy Fields."

Aelita's main power on Lyoko is her "creativity," which allows her to alter small portions of Lyoko's terrain at will. She can use the same power to create clones of herself, though they have limited functionality, acting in a per-determined manner. As mentioned earlier, Aelita also possesses the power to deactivate the towers on Lyoko, the main component in stopping X.A.N.A.'s attacks in the real world. Later on, Aelita is able to defend herself by generating pink orbs called "Energy Fields," which can destroy any monster on contact, regardless of where they hit, excluding Megatanks. Two energy fields can also be touched together to form a makeshift shield. Additionally, Aelita can charge her "Energy Fields" into a much larger ball of energy, which can do more damage than a normal Energy Field attack. Over time she also developed white feathered angel wings, which she uses for transportation; she can use them at her own will. At first, she could not be devirtualized normally as the others could, requiring a special program to bring her to Earth, but after that is able to leave in the same manner as the others.

Jeremie Belpois

Jeremie Belpois is the brains of the group and the youngest, directing their missions from the supercomputer and designing various programs to improve their chances of victory (though, as a recurring plot device, these programs almost always malfunction). Jeremie does not participate in the battles on Lyoko because he is needed back in the real world for technical support and to run the virtualization, devirtualization, and other computer programs in case of an emergency. He attempted to go to Lyoko one time in order to make amends with Aelita, and again to increase his resistance to XANA. He vowed never to return after the third time, due in part to his reportedly ridiculous-looking outfit and a poor experience with XANA's minions.) he turns 13 years old. He is in 8th grade. He is 13 to 14.

Jeremie has blond hair. He wears a blue turtleneck, brown pants and blue-gray shoes. He also has glasses, because he is nearsighted. Later on, his outfit is a dark red long-sleeve shirt, brown pants with light blue stripes going down the side of the legs, and dark blue shoes. His pajamas are dark blue.

Something of a workaholic, Jeremie invests the majority of his time into finding ways of stopping XANA, having spent the entirety of his free time trying to materialize Aelita onto the real world, and spent all of his free time trying to make an anti-virus after XANA infected her. Later on, he spends most of his time trying to find a way to virtualize the group into the Internet directly, until XANA possessed the newly inducted William and destroyed Lyoko. Later on, Jeremie receives a message from Franz Hopper, and manages to recreate Lyoko using the code sent to him. Later on, he spends the majority of his time locating Replikas, deciphering data from the Internet, and trying to free William from XANA. One of his major overall goals is to free Aelita's father, Franz.

He has a multiterminal computer of his own in his room, by which he develops programs, tests them prior to use within the factory's supercomputer, and at first, communicates with Aelita within the supercomputer. He uses a screen saver that closely resembles the "falling green letters" theme used in The Matrix series of movies, supposedly a homage. He has a black and white poster of Einstein.

Often, his determination to fight against XANA will take priority and he will leave his friends in the interests of working more. They rarely respond positively to this; however, he usually finds a way to make things up by the end.

Jeremie was the one who discovered Lyoko, as well as Aelita, and over time, he became very attracted to her. He is very attracted to Aelita's intellect, curiosity, and bravery, and although Jeremie can be shy at times, he has sought a romantic relationship with her, and it has been seen that Aelita feels the same way.

Jeremie has visited Lyoko a total of three times. Jeremie gets in an argument with Aelita, and later tries to go to Lyoko to apologize. He was, however, trapped in between Lyoko and the real world due to an error in the scanning process. XANA had created a sort of fake earth within Lyoko, trapping Odd, Ulrich, and Yumi. Jeremie went to this fake projection of earth and stopped XANA with Aelita's help, but he was devirtualized immediately afterwards and never actually went to Lyoko itself. Jeremie, Ulrich, and Odd came from Lyoko, where Ulrich jokes about how fast he was defeated by a Megatank. After that he said he would never go into Lyoko again. Jeremie's Lyoko form is seen he third time. His Lyoko form is the same as his form in the real world, and Ulrich describes it, tactfully, as "ridiculous."

Odd Della Robbia

Odd Della Robbia is the prankster of the group, acting less serious and more carefree than the others in any given situation. His attitude extends to most forms of danger, which Odd only seems to take seriously when responsible for the welfare of others. While Odd doesn't appear to be a serious student, he maintains a 75% average at one point, apparently aided by high art scores as well as his propensity to copy the papers of others during those tests he actually attempts to pass. During his free time, he prefers to work on guitar, film, drawing, other forms of art, as well as skateboarding, and trying to find his one true love. At first, he is 13 years old and in 8th grade. Later on, he is in 9th grade and is 14.

Odd has long hair spiked to a peak, with a splotch of purple in the center. Except for at first, in which he wore his hair down until after the first time he had been to Lyoko, calling it 'Lyoko style.'). The first of Odd's two outfits consists of a long-sleeve shirt and bellbottom pants, and platform shoes. His hair is styled into a large point in the same fashion as his hair on Lyoko. He also has a purple diamond on the front of his hair (which is naturally that color. Later on, his outfit consists of a purple hooded sweatshirt with a pink shirt underneath, purple bellbottoms, and dark red-orange shoes. His night clothes are red and yellow, not purple, and probably due to the fact he did not buy them (orange boxers/boxer briefs and a red shirt). Later on, Odd is able to be sent by Jeremie to a Replika computer to destroy it as a Spectre. While in this Spectre form, Odd closely resembles his fourth season Lyoko suit, except that he has three toe claws and his gloves end at elbow length instead of mid upper arm.

Odd considers himself to be something of a ladies' man, having managed to date almost every (similarly aged) girl at the school in the two years he's been attending it, sometimes two at a time. A recurring theme is Odd attempting to impress one girl or another, if he is not already dating them. He has shown a close attachment to a girl named Sam that doesn't attend his school, but these feelings might have changed as she withheld information from Ulrich about a XANA attack.

Another recurring theme, though less prevalent, are jokes about Odd's size in comparison to his eating habits. Despite eating two or three portions at every meal, Odd never gains weight or height, being the shortest member of the group, which is somewhat disguised by his platform shoes and hairstyle. The school nurse attributes this to Odd's high metabolism. His feet also smell.

Odd has a pet dog named Kiwi, which he keeps in his room regardless of the school's policy. Despite the rule against dogs, most of the students know about it. Odd also shares a room with Ulrich. The others have their own rooms or live at home. This occasionally results in arguments between the two on roommate-related issues. Later on, it is revealed that Odd has five sisters.

On Lyoko, he is dressed as a self-described "giant purple cat." The outfit is almost identical to the one he wears in the real world color-wise, but has no sleeves and is generally closer-fitting. To complete the "giant cat" motif, Odd only has four fingers (three digits and a thumb), complete with claws, and a tail. His forehead and cheeks also have purple markings on them. Later on, he receives a new outfit almost identical to the previous one, except being a slimmer full-body suit, with slightly altered highlights, and with cat ears in addition to his human ones. His vehicle is the Overboard, a similarly themed, two-tone, purple and pink hoverboard. His cat themed suit creates a bit of irony, seeing as he is presumed to be more of a dog person. On the front of his Lyoko suits (both of them) there is a picture of Kiwi peeing.

Odd's gloves are equipped with laser arrow launchers, which are his main weapon. Odd prefers to attack from long-range, using his accuracy to destroy monsters out of harm's way, but will often fight close-quarters in order to get a shot in. At first, he can only fire 10 arrows in one setting, but eventually gains the ability to fire as many as 10,000 with a reloading program created by Jeremie. Odd's powers vary between time. At first, Odd has future flash, the ability to see into the future though not at will and only for short periods. The ability was lost in the when Jeremie improved their abilities and described it "useless" despite the fact that it had saved them many times. In exchange, Odd gets an arm-mounted energy shield which appears when he summons it. His claws also allow him to climb up objects with ease. Later on, Odd temporarily gained the power to teleport, but the program bugged up, causing him to duplicate himself both where he was when he teleported and where he teleported to. This led to particle disintegration after an extended period of time, thus forcing Jeremie to remove the power. Odd also gives a name to almost every new Monster XANA creates.

Yumi Ishiyama

Yumi Ishiyama is the oldest member of the group and Hiroki's older sister, being one year older than the others and is of Japanese descent. Branching from this, she owns a suit of samurai armor handed down the generations she treasures very much, as well as being seen with aTotoro plushie in her room. Although sometimes a bit short-tempered, Yumi is very clever and cares greatly about her friends. Yumi varies between reasonable and stubborn at various points; though willing to reveal the supercomputer to the police in order to prevent a nuclear explosion, it takes the destruction of most of Lyoko to convince her to let William Dunbar join the group. At first, she is 14 years old and in 9th grade. She turns 15 later on. Yumi's hair is half-long black, headed back and sides. At first, she wears a black turtleneck, darker black jeans, and gray-black sneaker boots. Her hair is usually left hanging down. Later on, her outfit is slightly lighter but still mainly black, consisting of a long-sleeved shirt with an extra large neck hole. Her pants cut off halfway between her ankles and knees. Her shoes are pinkish reddish sneakers.

In terms of character development, the two major themes revolving around Yumi are her relationship with Ulrich Stern and her parents' unstable marriage, the former of which is the central focus. Yumi's relationship with Ulrich remains platonic, though they almost kiss and decide to keep it a secret from everyone else. After discovering her real romantic feelings for Ulrich,Yumi decides to outwardly declare their relationship to be just friendship. A first, she seems to have decided to hide her real romantic feelings for him, though later on, implies the two eventually explore their close romantic relationship again.

Later on, the story introduces Yumi's younger brother, Hiroki. He constantly teases Yumi about being in love with Ulrich. Most of the time, Yumi acts as if she can't stand Hiroki, but certain times show that Yumi does care for him.

Yumi's outfit is modeled after those worn by geisha. Her outfit consists of a short-sleeved/hemmed kimono over red tights, black thigh-length boots, red eye liner, red blush on her cheeks, a white-painted face and neck, and some red on her lips to complete the look. She also has a yellow sash tied to her back. Her hair is bunched up into a small bun with three bangs left hanging. Later on, Yumi gets a new, ninja-like outfit. It consists of form-fitting, pink and purple body suit with flowered shoulder pads, but retains the yellow sash from the previous one. Her hair is worn down instead of in a bun. The geisha makeup is less prevalent with the new outfit, though it's more apparent with her 2D model. However, she has two strange pill-shaped objects above her eyebrows. These are used to focus her telekinesis better. Yumi uses the Overwing, a hovering scooter, for travel on Lyoko. She usually shares this vehicle with Aelita.

Yumi's main weapons on Lyoko are her dual metal fans or Tessen (Samurai metal fan) that function like razor-sharp boomerangs when thrown. In flight, they turn into fast-moving, saw-like discuses, and also serve as shields to block enemy laser fire. Later on, her fans now appear and disappear at her will (as long as they are in her hands). At first, she only has one large fan, but later on, she has two slightly smaller ones. She also has telekinetic powers, though they are difficult to use and exhaust her quickly. However, later on, her telekinetic abilities are strengthened greatly. She is much more relaxed while using it and can use it in conjunction with her dual fans to telekinetically control the movement of her tessen fans in mid-flight.

Ulrich Stern

Ulrich Stern is the silently-strong introvert of the group, unwilling to talk about himself unless prodded considerably. Ulrich has brown hair. At first, he wears a light green shirt with a vest over it and cargo pants, all varying shades of green, and white shoes. Later on, his vest is replaced by a black shirt and army jacket, his white shoes are replaced with black shoes, and his cargo pants are replaced with blue jeans. His night clothes are green boxers/boxer-briefs with a white sleeveless shirt. Later on, the Warriors can be sent to Earth as spectres to destroy XANA's Replika computers. His Spectre form is much like his Lyoko form, except the sleeves end at mid upper arm and the headband is yellow with a white circle on his forehead.

At first, he is thirteen years old and in 8th grade. He is in 9th grade and is fourteen years old later on.

Ulrich doesn't say much about his personal life and is evasive when someone asks him about himself or his family. His parents, his father in particular, are very hard to please and have high expectations for their son. He also has trouble expressing his feelings, mainly where Yumi Ishiyama is concerned. He really romantically loves Yumi and tries to express his true strong romantic feelings but Sissi always gets in the way of the both of them. A common theme is Ulrich only admitting to something after a brush with death or an otherwise die scenario. In addition to his troubles with Yumi, Ulrich has to deal with Sissi's affections. Due to her being the daughter of the principal, he is often forced into humoring her in order to get something from her father.

Ulrich sees William Dunbar as his rival in their race for the affection of Yumi and can get often very jealous at him. Although, he doesn't know that Yumi Ishiyama really loves him but keeps her feelings locked in.

Ulrich's Lyoko attire is modeled after a samurai, minus armor, and he carries a sword. An Oni is drawn on his back and the clothing is largely colored yellow and black. He gets a new outfit later on, which trades his more loose-fitting clothes for a tighter yellow and brown body suit (similar to William's). A device on his back is traded for his sword sheath, which, in addition to carrying two swords, hides the blades when they're not in use. For travel, he uses a one-wheeled motorcycle called the Overbike, which is also capable of flight.

Ulrich's katana allow him to cut through monsters with ease or deflect enemy laser fire. His speed on Lyoko is enhanced, such that he can deflect even rapid laser fire with relative ease and run faster than most monsters. An additional boost to his speed can be gained through a super-speed running ability (called Supersprint), which can be used to easily traverse long distances, and even cross the surface of water. He can create two clones of himself to aid in battle (called Triplicate), each of which can take one hit before being destroyed. He can bring these clones back together into him (called Fusion). He can also summon his clones to make a triangle around his enemy, (called Triangulate) then attack it when least expected. Both he and Yumi are practitioners of Pencak Silat.

William Dunbar

William Dunbar is first introduced later on as a new student at Kadic, having been kicked out from his previous school for plastering love letters everywhere,and glueing stickers on the principal's winshield. William has very short, dark and unnatural dark blue hair. William's first outfit consists of a short-sleeved black shirt with a long-sleeved red undershirt, blue jeans and boots. His outfit  later on consists of dark-blue pants, a black shirt with a red logo, and a tan jacket to replace the red undershirt. At first, he is 14 years old and in 9th grade. Later on, he is 15 and in 10th grade, just like Yumi.

William serves as a foil for Ulrich, both in his attraction to Yumi and outspoken personality. While Ulrich has trouble sharing his feelings with Yumi, William isn't afraid to assert himself. He spends most of his time trying to get closer to Yumi, which puts him at odds with Ulrich. He is the secondary antagonist in and primary antagonist under XANA.

Eventually William learns of Lyoko and XANA, and tries to join the group several times, only to be rejected. William joins the Lyoko warriors later on, but is quickly possessed by XANA after he is attacked by the Scyphozoa. XANA then uses William to destroy Lyoko. With Lyoko destroyed and Jeremie cut off from him, William's mind and body is left at the mercy of XANA, who forcibly possesses him to be his servant, giving him a new black XANA-themed suit and powers. From this point until his final freedom, William is helplessly kept under XANA's control, battling the Lyoko warriors. XANA uses William to command his monsters in battles to even the odds. He even uses a unique Manta, which is colored black instead of the standard blue, as a vehicle for William on Lyoko. He is freed from XANA later on, but the group is wary to trust him again. He has no memory of anything that happened during his possession. XANA again possesses him in "Fight to the Finish", and he is once again freed once XANA is destroyed.

At first, William's Lyoko attire consists of a white and blue form-fitting bodysuit with a red belt. After he is taken over by XANA, his outfit changes to a similar, all-black outfit with red outlines and the eye of XANA on his forehead and chest, as opposed to his eyes. He also gains a spiked gauntlet on his left arm capable of blocking attacks.

As XANA's servant, William's primary ability is smoke manipulation, reflecting XANA's use of smoke-like ghosts in the real world. His weapon forms from smoke and is reduced to such when not in use, which allows him to call the weapon back if they are separated. William can also reduce himself to smoke, allowing him to move at high speeds, and can quickly transform back upon reaching his destination. Finally, he can create smoke in his hands and fire it at his opponents to restrain them, after which he can use the smoke to achieve a limited form of telekinesis on his target. Other powers include hovering and long-range vision.

While possessed, William doesn't devirtualize when dealt enough damage. Instead, he is reduced to glowing red smoke which dissipates into the ground. Additionally, while William usually needs only one successful hit to devirtualize the Lyoko warriors, it takes either several hits or one fairly powerful attack (being cut in half or stabbed in the chest) to do the same to him. It takes one charged energy field to devirtualize William.

X.A.N.A.

Created by Waldo Franz Hopper, X.A.N.A is a multi-agent computer program and the primary antagonist of the show. It's a computer program, that has somehow become alive and sentient, and uses its powers of control over anything digital and electronic to cause enough chaos so that it is allowed time to escape the supercomputer. It seeks to take over the world, but often focuses its efforts on the group, seeing as how they foil most of its plans. Most of its attacks tend to be fairly straightforward with little or no warning beforehand. At first, X.A.N.A.'s attacks are directed mostly at humans in general. Later on, the attacks are centered around the group. XANA's favorite targets are Aelita and Jeremie, since they are the two most capable of operating the supercomputer. It is able to cause extreme chaos when it activates a tower, tall cylindrical buildings in Lyoko that, when activated, can give XANA a special ability, until the tower is shut off. Eventually, XANA escapes the supercomputer, and destroys Lyoko.

X.A.N.A. is represented by an red eye made up of a roundabout in the center besieged by two circles. Four tabs occupy the contour of the outermost circle: a longer than others at the top and three other shorter bottom equidistant from each other. The center is a bit wider.

XANA's main power is possession through an energy-based, ethereal "ghost," known as a "spectre", capable of possessing virtually any object and likewise modifying it to almost any necessary end. When a human is "Xanafied" or possessed by XANA, their eyes often have the Eye of XANA symbol (found on all of XANA's monsters) instead of pupils. His own ghosts can also manifest themselves as people without the need for a host as a "polymorphic spectre." Among the common abilities imparted by the ghosts are electricity control/manipulation, enhanced physical abilities, and apparent invincibility. Additional abilities include phasing through solid objects, self-replication, and technopathy.

XANA rarely speaks or communicates in any way, usually only doing so after he assumes a disguise (like the time he took the form of Jeremie and the two occasions where he took the form of Franz Hopper). He can also speak through the mouths of his "Xanafied" slaves, but he rarely does.

Like the Lyoko Warriors, X.A.N.A. is opposed to anything it sees as a threat, and on at least one occasion, this has led it to team up with the Lyoko Warriors; it was seen helping the group to protect Aelita from Jeremie's latest blunder, as it needs Aelita for her memory. Later on," X.A.N.A. is supposedly destroyed once and for all by Jeremy's multi-agent system due to Franz Hoppers' self-sacrifice.

Waldo "Franz Hopper" Schaeffer

Waldo "Franz Hopper" Schaeffer is the creator of the supercomputer, Lyoko, and XANA, as well as Aelita's father and Anthea Hopper's husband. He was once a science teacher at Kadic, having been replaced by Suzanne Hertz after his disappearance 9 years ago. He lived at a house near Kadic called the Hermitage with Aelita, and before that had a home in a mountainous region. Franz Hopper built Lyoko and XANA to destroy a military project called Project Carthage, which was designed to disrupt enemy communications. Lyoko was later adapted to serve as a sanctuary for him and Aelita, an apparent result of his suspicions that someone was watching him. Upon fleeing to Lyoko, however, Aelita and Franz were attacked by XANA. Franz unsuccessfully tried to reason with XANA, and when that failed he shut down the supercomputer, leaving it inactive until it was found nearly a decade later by Jeremy. Franz has gray hair, beard and moustache. He wears glasses and a white lab coat over a long-sleeved sweater.

Later on, Franz possesses Sissi to try to contact Jeremy. When she is possessed, at first, she seems to be speaking gibberish, but upon further investigation, it is revealed that she is saying backwards, "I can help you. I want to enter into contact with you now, I'm Franz Hopper. I can help you."

Franz is variously depicted in Lyoko with sphere-shaped constructs. Later on, he is depicted as numerous white spheres, while his appearance later on is that of a larger purple sphere. Franz Hopper, like XANA, can reach out to the real world through the use of the towers, but not nearly as effectively as XANA can. He helps the warriors at various points in the series, even helping them to recreate Lyoko after its destruction. Later on, his true name is revealed to be Waldo Schaeffer, while "Franz" is actually his middle name and "Hopper" is his wife Anthea's maiden name. Later on, he sacrifices himself to give Jeremie's multi-agent system enough power to completely wipe out XANA. The act creates a sense of irony, considering that the majority of the series was spent trying to rematerialize him.

Sissi Delmas

Elisabeth "Sissi" Delmas is the spoiled, arrogant, and in some ways selfish daughter of the school's principal, Jean-Pierre Delmas, and considers herself to be the most attractive girl in school. She is a former heerleader, has shown to be a skilled baton twirler, and once used a baton as a striking weapon and a club. She prefers to be called Sissi, and usually becomes angered whenever someone uses her full name - on fellow students, however, she uses physical violence. She is attracted to Ulrich (who has no feelings for her in return) and is jealous of Yumi (whom Ulrich is attracted to). Multiple times, she is seen stalking Ulrich, much to the annoyance of Team Lyoko. Undoubtedly snobbish and a spoiled child, at first, she only rarely showed a more empathic side, mainly when the lives of others were in danger. She lightens up later on, and sometimes helps the group achieve victory, though she's not quite aware of the extent to which she helps. She admits  that all she wants is to be accepted by Jeremy and the others, which she gets later on after discovering the factory and making a scene about it. The group uses a return trip to wipe her memory then accepts her to keep her from following them anymore and as a means of thanks for the various occasions she's been of help in the past, with Odd stating that school would be boring without her. It is eventually revealed later on that Sissi took Pencak Silat classes to impress Ulrich, but it didn't work. However, later on, her skills in martial arts had been dumbed down significantly. She was originally a member of the gang when they first discovered Lyoko and was intended to join them, but they decided to kick her out after she ratted them out during XANA's first attack. They used the return to the past and wiped her memory of the event and never again informed her of it, certain she would again reveal their secret.

At first, Sissi wears a yellow hairband on her head which pulls her long raven hair back. She is dressed in a pink t-sleeved shirt with a yellow heart on it and usually the shirt's hem stops right about an inch above her belly button, which is very ticklish, and a dark pink mini skirt over red/purple trousers with pink shoes. Later on, she does not have the hairband (replaced by two hair clips) and has a pink t-shirt with light blue jeans and red shoes. Later on, she is seen with the same outfit only a yellow shirt with a pink heart due to X.A.N.A.'s errors in the false world of Earth.

William Clone

William Clone was created by Jeremy to fill in at school so no one would know that the real William was gone. The clone wasn't very smart though. It had enough common sense not to do dangerous things, and it would answer insults in a very plain fashion, not getting mad as it didn't know what the person meant. It had no emotions aside from confusion and happiness. So it would say the logical answer to jokes. This would often confuse people, occasionally with humorous results, as those around him believed William was playing dumb. He was created by Jeremie Belpois. He is in 9th grade.

Later on, it was shown to demonstrate rage. The real William, possessed by XANA, returned to the real world and attacked Milly and Tamiya (who had found the factory and were inside the control room at the time) because they got in the way of XANA's plan. During this time the clone protected them using abilities equal to possessed William (super speed and strength etc.), performing well against the original until XANA-William hacked into Jeremy's console and deactivated his program, causing it to disappear.

The first time Jeremy made a clone was later on and the clone was of himself to fill in at school so he could work longer. He succeeded activating a tower for the first time. It worked for a while, but XANA-William attacked the tower in attempt to take control of the clone, and the Lyoko warriors, in new suits and weapons that Jeremy had been working on, were sent to stop him. They managed to defend the tower and stop William. Aside from that and having to explain everything to it, the clone of William after that worked just fine. Jeremy later put up a defense program to prevent XANA from further attempts at taking control of the clone.

The only other recorded time XANA took control of the clone of William was when Jeremy had written a program to free the real William, but it malfunctioned and bugged up the defense program on the tower maintaining the William clone in the real world. At this point XANA had XANA-William go and corrupt the tower so it (XANA) could take control of the clone. The possessed William did succeed, with a resultant attack on the team in the real world. In the end the team managed to fix the tower and thus the clone. They returned to the past to keep Lyoko and the clone of William a secret.

Later on, the team had finally saved real William from XANA returning him to the real world, where William’s parents had shown up for a visit, which wasn't going well. William's parents had become suspicious of the clone due to its strange behavior and abnormally happy disposition, which were opposite of their experience with him. When the team and William got to the clone and William's parents, his dad had just declared that he (the clone) wasn't his real son, as he was too happy and totally obedient. The real William was kicked out of one school because he put stickers all over the Principal's car. The team distracted William's parents and Principal Delmas, and while they weren't looking Jeremy deactivated the clone causing it to disappear. At which point the real William quickly took its place, and acted like himself, getting his parents to calm down and clearing everything up (without anyone knowing about the clone). Jim was the only person who saw the clone disappear, and of course didn't understand what had happened.

Jim Morales

Jim Morales is the Kadic physical education teacher, handyman, chief disciplinarian, Pencak Silat instructor and campus/dorm moitor. He has worked at the school for twenty years, as Jim states later on. As campus supervisor and PE teacher, his job is to make sure that the children follow the school's myriad of strict rules, but he ends up acting ridiculous and clumsy at every turn; when the students do break the rules or incur his ire, he usually (in a very angry tone) threatens them with some form of disciplinary action, such as grounding Milly and Tamiya to their room for wandering into the tool shed when they were only trying to reclaim Milly's teddy bear - however, Milly herself says in the same scene that he believes everything is off-limits to the kids. He is also the prime target for school pranks. When XANA launches attacks against the schoolchildren, his attitude shifts to that of a kind and loving protector. His nickname is Jimbo, which is something he claims that his friends used to call him when he was the students' ages.

In addition to his jobs at Kadic, Jim has apparently served under a wide variety of occupations, such as an army soldier and an actor. However, any attempt to get him to elaborate on his past occupations is usually met with his trademark catchphrase answer of "I'd rather not talk about it." He has a nephew named Chris, who is the drummer for the Subdigitals. He also has an interest in Suzanne Hertz, hinting at possible feelings between the two teachers.

Jim is also the only person, aside from William Dunbar and Sissi Delmas, to have known the secret of Lyoko and the gang (for more than a very brief period of time). Later on, He accidentally gets Jereme injured during a chase scene. The principal found them and fired Jim. Jeremie and the crew took pity on Jim and told him everything, even allowing him to live in the factory for a short time. He proved to be very valuable when XANA materializes his monsters into the real world, where Jim met them with a nail gun and managed to protect the Kadic students in the real world while the rest of the gang went to Lyoko to deactivate the tower. Afterwards Jeremie did a return to the past which took everyone back to before Jim was fired and erasing his knowledge of Lyoko.

Jim's hair is quite short,brown, and pulled back somewhat by a  sweatband around his forehead. He also wears a bandage on his cheek, which he has never explained. Jim wears a white short-sleeved t-shirt, concealed under a dark red tracksuit jacket which covers all his upper body and his belly, along with dark gray jogging pants and brown sneakers. Other than his overweight stomach, Jim's arms are muscular.

Jean-Pierre Delmas

Jean-Pierre Delmas the headmaster and Sissi's father. He once fired Jim for injuring Jeremie, believing that Jim did it intentionally. Odd names his Tamagotchi after him. Later on, he often spends all of his time playing on his computer.

Nicholas Poilakoff and Herb Pichon

Nicholas Poliakoff and Herb Pichon are two teenage boys who also attend Kadic Academy. They both follow Sissi Delmas around acting like her "pets". Although it is clear that Herb Pinchon has deep feelings for Sissi, it is clear that she does not feel as strongly. Rather, she tends to keep them around when she needs company, but as soon as Ulrich and his gang show up, they are thrown away.

Herb Pinchon is rather smart and it is revealed that he has Claustrophobia.

Nicholas is also a very talented drummer as seen when he wants to join the Lyoko Warrior's band.

Kiwi

Kiwi is Odd's dog, who boards with him at Kadic academy, even though dogs are not allowed. Kiwi once was possessed by XANA; he traveled around the school and infects various students and teachers by biting them and turning them into zombies. Ulrich also went into Kiwi's body. In "Dog Day Afternoon" Odd tries to take Kiwi to Lyoko, but ends up absorbing the little dog instead. As a result, Odd slowly begins to take on dog traits, such as enhanced smell and scratching himself with his foot.