List of Code Lyoko characters

Protagonists

L to R: Aelita, Ulrich, Yumi, Odd with Kiwi, Jeremy.

Jeremy Belpois

Jeremy Belpois (previously Jeremie, voiced by Sharon Mann) is an exceptional student enrolled at the fictional Kadic Academy. He once lamented his normal, average life before discovering the existence of Aelita and subsequently becoming infatuated with her. Afterwards, he takes it upon himself to materialize her in the physical world at any cost. He begins recruiting his schoolmates to fight on the virtual world of Lyoko in order to defeat the malevolent AI, XANA.

Aelita Schaeffer

Aelita Schaeffer (voiced by Sharon Mann) initially believed to be an artificial intelligence by Jeremy Belpois, is a soft-spoken, amiable child who was confined on a supercomputer located near Kadic Academy before being unintentionally rescued by Jeremy. As a child, her father, Franz Hopper, helped Aelita escape from a confrontation with several government agents via hiding her on his supercomputer; this action causes her to lose the memories of her life as a human being. It is only after she is materialized on Earth that she begins to realize that she is, in fact, human. On earth, she adopts the pseudonym surname "Stones".

Ulrich Stern

Ulrich Stern (voiced by Barbara Weber-Scaff) is the first character to be recruited by Jeremy in an effort to combat the newly discovered XANA. An antisocial youth with passing grades, he frequently displays angst arising from conflicts with his somewhat overbearing parents and academic admonishment. Despite this, he remains a focal member of the group. He also has a crush on Yumi.

Odd Della Robbia

Odd Della Robbia, voiced by Matthew Géczy, is the second character to be recruited by Jeremy and the first person he sends to Lyoko, although unintentionally. The roommate of Ulrich, Odd is a hazardously carefree individual, displaying very little concern for his own safety. Odd is an extroverted, flamboyant prankster who fancies describing himself as "svelte". He demonstrates that he has anxiety towards his parents due to his perception that they are "too perfect".

Yumi Ishiyama

Yumi Ishiyama (voiced by Mirabelle Kirkland) is an older student of Japanese descent attending Kadic Academy. Cautious and mildly pessimistic, Yumi is often a more mature voice of reason amongst her friends. She displays fierce sibling rivalry with her younger brother, Hiroki, often hiding her affection for him. She is the third character to be recruited by Jeremy. She has a crush on Ulrich just the same as he has a crush on her.

William Dunbar

William Dunbar (voiced by David Gasman) is the fourth and final child in the series to be recruited by Jeremy in an effort to defeat XANA. William is an overconfident student at Kadic Academy who often fights Ulrich for Yumi's attention. Despite his rifts with the protagonists, he becomes the closest thing to a trusted ally they have. Although Jeremy, Ulrich, Odd, and Aelita initially voted in favor of his joining them, they were unable to reach consensus due to Yumi's disapproval.
Eventually, however, the vote becomes unanimous that William's membership is necessary. On his first mission in Lyoko, he is captured and possessed by XANA, who ensnares William as its puppet.
From this point on, a clone of William, created by Jeremy, is used to pose as the real William until Jeremy is able to free him. Unfortunately, Jeremy's program is extremely malfunction-prone, causing the William clone to act either abysmally unintelligent or unpredictable and dangerous.

Antagonists

XANA

XANA (also spelled as X.A.N.A.) is a malicious artificial intelligence that serves as the main antagonist of the series. It was originally programmed by Franz Hopper in the 1990s designed to destroy Project Carthage - software that Franz Hopper had previously been closely involved with. He mentions that his motives were to prevent the French government from obtaining access to Project Carthage. Unfortunately, due to his repeated returns to the past, XANA eventually became sentient; choosing to rebel against Franz. It then trapped Franz and his daughter Aelita inside Lyoko. Luckily, Franz was able to shut down the supercomputer to trap XANA and prevent it from wreaking havoc in the real world, such as possessing humans, animals, items, environments, and many other forms such as gravity.
XANA displays no mercy whatsoever towards those who stand in its way, waging attacks through Lyoko structures known as towers into the real world, often attempting mortal harm against the protagonists. It usually employs monsters inside Lyoko in order to prevent the heroes from deactivating the towers and ruining its plans. It also has the ability to manipulate electrical devices and control living beings through possession. Whenever a human is possessed by XANA, that person is given enhanced strength and speed, alongside electrokinesis, technopathy, and the ability to phase through solid matter.
Being an AI computer program, XANA has no actual physical form. Despite a symbol called the Eye of XANA constantly symbolizing its presence, it never actually confronts the Lyoko Warriors in person. It is speculated that its monsters are actually part of XANA itself, but is still unconfirmed.
The only known physical incarnation of XANA appeared in the Season 1 episode "Ghost Channel"; where after having its disguise as Jeremy being exposed, it transformed into a demonic caricature figure of him and tried to kill all of the warriors. XANA's voice was provided by David Gasman in this episode.

Supporting characters

Franz Hopper

Franz Hopper, also known as Waldo Schaeffer, voiced by Paul Bandey and Alan Wenger, is the creator of Lyoko, XANA, and was involved in the creation of Project Carthage. Formerly a science teacher at Kadic Academy, he vanished suddenly while living in a house in the school park called the Hermitage. In a nearby abandoned factory, he constructed the supercomputer on which he created Lyoko, only to be intercepted by XANA during his and Aelita's virtualization. Franz was forced to shut the supercomputer down, until it was discovered by Jeremy Belpois nearly ten years later.

Jim Morales

Jim Morales, voiced by David Gasman, is the physical education teacher for Kadic Academy, although it is never explicitly revealed what his entire occupational history is. His meticulously half-secretive past, which may or may not be accurate, is one Jim is particularly proud of, typically digressing from his lectures in order to reminisce on stories of his youth.
Jim is often suspicious of the protagonists, despite wishing to be friends with them.