William Wharton was a multiple murderer. It was later discovered, that he also killed the two girls, for which John Coffey was convicted and later executed of. He is a madman, who likes to hurt, mistreat and annoy others. That´s why the wardens have to take drastic measures in order to control and subdue him, while he is in death row.
A few trademarks include: A Billy the Kid Tattoo on his arm and knowledge of Wild West history. The latter of which, he says when Brutal intentionally calls him Wild Bill, prompting him to go berserk and mention the difference between Wild Bill Hickok and Billy the Kid. He also seems to be an attention hog as he fears the padded room, for it's isolation.
John kills him through one of his wardens, Percy Wetmore, for what he did.