Thief is a class with abilities like
Backstabbing: You may discard a card to backstab another player(-2 in combat ). You may do this only once per victim per combat, but if two players are fighting a monster together, you may backstab each of them.
Theft: You may discard a card to try to steal a small Item carried by another player. Roll a die; 4 or more succeeds. Otherwise, you get whacked and lose a level.