Who is Cripple Wa from Mort and what is their importance?

Cripple Wa is the sponsor of a famous floating crap game in Ham Alley, Ankh-Morpork. Death, on a winning streak, makes a wager with Wa. If he wins, Wa will stop insisting that chance governs the affairs of men. If he loses....... he will wish he had won. Wa throws three eights and falls over in a faint.