XANA

""In the very beginning, it was a program that I designed to counter a military project, based on a multi-agent system.""

- X.A.N.A. himself while posing as Franz Hopper.

X.A.N.A. is a highly advanced supercomputer and the main antagonist of Code Lyoko. He was voiced by David Gasman.

Origin
X.A.N.A. is a emotionless computer created by Franz Hopper/Waldo Schaeffer based on a military project along with Lyoko itself. However, the program went haywire and got out of control, which caused both Hopper and his daughter Aelita to be virtualized into Lyoko. Also, X.A.N.A. became megalomaniacal, vowing to destroy mankind and Hopper while gaining Aelita's memories to escape the supercomputer he is bound to.

Attacking the Real World
X.A.N.A. repeats the same strategy every time: activating one of Lyoko's towers and initiating an attack on the Real World, which is detected by Jeremy's alarm. He then leads the group to the factory and sends them to Lyoko with Aelita to deactivate the tower while one or more members stay behind to fight the evil X.A.N.A. is causing. After the tower is deactivated, Jeremy initiates a "return to the past" to erase everyone's memories (except for themselves) of the incident. However, after the second season, X.A.N.A. finally manages to destroy Lyoko and Aelita, escaping the supercomputer in the process, but he is again caught and returned to the virtual world by Franz Hopper himself, who is revealed to be Aelita's father. In another point of the series, the computer fully brainwashes Yumi's friend, William Dunbar, into being his minion .Eventually, Jeremy manages to save William with Franz Hopper's help and also rebuilds Lyoko while giving the group new outfits and abilities.

Final attack and death
X.A.N.A.'s final attack begins after Jeremy realizes that they must destroy X.A.N.A.'s supercomputer structure and finally kills the connection between Aelita and the computer so it can be shut down. When William is back, Hopper contacts Jeremy from Lyoko, giving him the necessary multi-agent program to finally kill the supercomputer. However, X.A.N.A. is not willing to go down without a fight and activates a tower to possess William once again, while the rest of the group goes to Lyoko to start the program and Yumi stays behind to fight the Xanafied William. After many devirtualizations, Aelita manages to activate the program while Hopper is killed in the process, finally stoping the possession and destroying X.A.N.A. once and for all. At the end of Echoes it is hinted X.A.N.A may have been revied or had a back up file because the super computer glows as if turning itself back on possibly because of him and since there is a season 5 upcoming in 2012 (Code: LYOKO Evolution), XANA could be brought back.

Character and powers
X.A.N.A. is incredibly strategical and calculist. He knows everything about science and technology, but his biggest focus is on the group that is always trying to stop him. X.A.N.A.'s main method of attack in the Real World is through possession using a ghost-like being to do it. The ghost can possess and modify mechanical objects and also possess living beings like plants and animals, and humans. When a human is possessed by X.A.N.A. (or "Xanafied", "Xanatifié" in French), the possessed's eyes will start to show the computer's symbol, the "Eye of Xana". The person will also display enhanced agility and strength and twitch like a hologram, while using electrokinetic powers and being able to walk through walls. The ghosts can also take a physical form of any kind to deceive and attack the group, and possess entire locations, such as Kadic's cafeteria and the factory itself. In Lyoko, X.A.N.A. uses a massive army of monsters to fight the protagonists, each with diferent shapes and powers, but one common weak spot: the Eye of Xana symbol in their heads.

Physical incarnation
In the 1st season episode "Ghost Channel", we get to see a physical manifestation of XANA himself aside from his specter form in the last episode, and possibly the only time he assumed a human form himself and/or faced the main characters directly. In Jeremie's form, XANA's eyes are completely white and his hair is upwards. His hands are almost skeletal in appearance, and he speaks with a deep, evil voice that resembles that of character Jim Moralés (also voiced by Gasman). This is possibly XANA'S real voice, as whenever he possesses someone, said voice can be heard underlying that of the character's when they speak. The episode also reveals that XANA doesn't seem to understand human emotions or human nature too clearly, as he shouts that is not logical for the characters to know who the real Jeremie is based only on their friendship.