Excerpt from the Code Lyoko Wiki: William has a strong personality. Being a fighter, he doesn't hesitate to let things get messy with Ulrich when he provokes 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.