Billy Jessup is the secondary antagonist of Jumanji. He was an enemy of Alan Parrish when they were kids.
Billy has been/is one of Alan's enemies since he is/was a child. Between the two does not flow good blood, as he was the boyfriend of Sarah, when they were children, while Alan and the girl, have always been good friends, and this has never liked to his boyfriend. We can say, that was Billy, one of the causes, for which Alan was trapped, for twenty-six years in the game,since it's Billy and his friends fault, if Alan had to hide at the factory,so as not to be beaten by them.