Wolfgang constantly torments Arnold and the other fourth-graders, and is seen as sort of his rival when it comes to sports. He's also very superstitious as seen in Friday the 13th, as he becomes easily spooked when Arnold's Grandmother brings her dozen black cats.
He gets his main kicks off of winning and demeaning those smaller than him. Supposedly, Wolfgang was created when the show creators discovered between Seasons 1 and 2 that Toran Caudell's voice had changed to the point where he couldn't talk like Arnold anymore. He is 10 or 11 years old.
Wolfgang was voiced by Toran Caudell, who formerly did the voice of Arnold.