Code Lyoko is a French animated television series created by Thomas Romain and Tania Palumbo. The series centers on a group of five teenagers who travel to the virtual world of Lyoko to battle against a malignant artificial intelligence named X.A.N.A. who threatens Earth. The series is presented in both traditional animation and CGI.
The series began its initial ninety-seven episode run on 3 September 2003, on France's France 3, and ended its run on 10 November 2007. In the United States, the show was first broadcast on 19 April 2004, on Turner and Time Warner's Cartoon Network. The show returns with a live-action reboot series, Code Lyoko Evolution, which began in late 2012, changing the traditional animation to live action and keeping the 3D computer animation while in Lyoko.
Code Lyoko tells the story of four boarding school students enrolled at Kadic Academy: Odd, Ulrich, Yumi, and Jeremy, who discover an artificial intelligence unit, Aelita, who is the sole inhabitant of a digital world known as Lyoko. An evil program of the Supercomputer that houses Lyoko, X.A.N.A., plots for reasons unknown on destroying all humans on our fair planet. X.A.N.A. attacks Earth by using towers to hack into electronic devices, possess objects, or take control of non-sentient organisms. Our four heroes must then escort Aelita to the activated Tower, where she deactivates it, and saves humanity in the process. During this time the main characters deal with their school lives, fall in love, become rivals, yell at each other, go crazy, and generally deal with their split lives.
The plot of Code Lyoko centers around five humans, Jeremy, Aelita, Odd, Ulrich and Yumi and the antagonist, X.A.N.A.. Of course, there are various secondary characters worth mentioning, such as William, Sissi and her lackeys (Herb and Nicholas), Jim, Milly, Tamiya and various background characters who also provide interesting plot twists, such as Franz Hopper (father of Aelita), Anthea Schaeffer (mother of Aelita), Taelia (specially in season 5) and Samantha Knight.
In the season 1, the sole purpose of the Lyoko Warriors was to materialize Aelita and shut down the Supercomputer so that X.A.N.A. would not interefere with the outside world. They achieved this Code: Earth, however. X.A.N.A. planted a virus in Aelita which killed her if the Supercomputer were to shut down.
In the season 2, following the revelation that Aelita had a virus inside of her, the group continued fighting in search of a “cure” for Aelita. However, with the introduction of Franz Hopper and Sector 5, the group's goals were increased. It was gradually revealed that Hopper was Aelita's father, and that he built Lyoko as a sanctuary for Aelita and him, and X.A.N.A. was originally a program to destroy Project Carthage, a military program that involved his advances in time travel. X.A.N.A. eventually escapes during an attempt to cure Aelita by completely wiping out her memory and thus killing her. Hopper however appears and revives her and restores her memory. X.A.N.A., now free from Lyoko's boundaries, is now located on the web.
The season 3 features Jeremy trying to figure out how to access Sector 5. X.A.N.A. is still sending attacks, however these attacks are more powerful and strong as he is now in the web. Throughout the season, X.A.N.A. attempts to wipe out the four sectors to prevent the team from accessing Sector 5. He eventually does through a possessed Aelita, by wiping out the sectors one-by-one. William joins the team so team has better changes to fight X.A.N.A. He however gets captured and possessed.
In the season 4, the group has a whole lot on their list: rebuilding Lyoko, recovering William, traveling the web in search for X.A.N.A., trying to cover up William's disappearance, finding Franz Hopper, along with the everyday issues of school and life. Through the course of the season, these goals are fulfilled however with the cost of Franz Hopper's life and a handful of questions left unanswered. Since X.A.N.A is now scattered around the Digital Sea, the team is now faced on how to counter X.A.N.A. As Jeremie works around the clock to find a solution, he finally comes up with the idea of a virtual submarine, named the "Skidbladnir". With the Skidbladnir all programmed and ready to go, the Team decides to hunt down X.A.N.A on the network as to bring William and Waldo Schaeffer home. In the maiden voyage, the team stumbles across an unknown sphere. However, the team later realizes that this was not in fact Lyoko. They later return to this mysterious sphere and realize it is an exact copy of Lyoko, except that instead of housing four sectors, it houses just one. These “Replikas” are housed the same way as Lyoko is: inside a supercomputer. During this time, Jeremie programs a way to bring them to the real world as spectres to destroy supercomputers that house the Replikas.
In the fanon season 5, they're trying to piece together X.A.N.A.'s return. Sissi discovers the supercomputer and the lab on the factory, but she's possessed by X.A.N.A and she goes to Lyoko under X.A.N.A.'s control. The Lyoko Warriors discover more Replikas, and the new X.A.N.A's home, called Xanadu. William leaves the series. Now the Lyoko Warriors have to recover Sissi, and destroy X.A.N.A. again.