William Dunbar is a major character from Code Lyoko. joined Code Lyoko in the second season as one of Yumi's classmates. In Final Round, he became the sixth member of Lyoko Warriors, until his first trip into Lyoko, when X.A.N.A. possessed him and used him as his general until episode Down to Earth where he was freed and returned as an ally. He then returns in Code Lyoko Evolution, and permanently joins the team at the end of the episode Rivalry.
William is a transfer student exiled to Kadic Academy in Season 2 for spamming love notes. His primary function during the first half of his tenure is to act as a Romantic False Lead for Yumi and lampshade Ulrich's inability to spit it out in the process. William's assistance in foiling several of XANA's schemes on the real-world side proves critical in Season 3, though, and after he confides to the Team that he is starting to dream about elements of his adventures that should have been erased with the Return to the Past, the Lyoko Warriors reluctantly (but unanimously) take him on as their newest member. It goes downhill from there. Mind-controlled by XANA (and stripped of his higher vocabulary in the process), William spends the majority of Season 4 as the Lyoko Warriors' most consistent virtual threat.