William Dunbar joined Code Lyoko in the second season as one of Yumi's classmates. In Final Round, he became the sixth member of Team Lyoko, 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.
Personality and Character
William has a strong personality. Being a fighter, he doesn't hesitate to let things get messy with Ulrich when he's provoked by him in A Bad Turn. He says that love can drive him crazy, and it's true, because he jumps at the chance to go out at night, against the rules, to visit Yumi. He's a hopeless optimist, he continues to follow Yumi even when she seems to be fed up with him, but he is also extremely curious, unfortunately for the group.
Sometimes he is childish, the best example is in Final Round. In these cases, his immature side is clearly seen, but this aspect of William is also obviously present in his provoking side.
But his strong point, which catches the group's attention, is that he is really brave. In Lyoko Minus One and The Secret, he fights against his entire possessed class and a construction worker who is also under X.A.N.A.'s possession. He deactivates a bomb with seven seconds to spare. William also has great mental strength. In the whole series, he is the only character who has fought X.A.N.A.'s influence while being under his control in The Lake. So, prowess is a word that can be attributed to William's character, but it's not the only one; he's also very frank and doesn't mince his words. He's also serious, but some of his actions are ridiculous, like for example his puerile reaction during his first virtualization, or his repeated flirting attempts.
There is a universal trait among all the character's good and bad qualities: he is persevering. In the end, however, this is what makes him touching: when he became himself again, the heroes rejected him tactlessly, and yet he still wanted to lend a hand if they needed it. That's why, although William can be blamed for many things, there is still good parts inside him.