Duke Leonal Felmet ruled the kingdom of Lancre for a while after murdering King Verence I. He had a mind like a clock, and like that clock it regularly went "cuckoo". He married Lady Felmet for the power, but found that she kept it anyway. Murdering his cousin to become king drove him insane, leading to his death. Believing he was a ghost, he slipped on the battlements of Lancre Castle and dropped to his death in the river.
Duke Felmet's story draws from Shakespeare's Macbeth. Like the Roundworld version, Felmet's wife is infinitely more ambitious than her husband and she inspires him to murder the rightful king. However, in a characteristically neat twist, it is Felmet who loses his mind with regard to the blood that won't wash away. In Shakespeare's play, it is Lady Macbeth who repeatedly washes her hand to rid herself of the stain: Will all great Neptune’s ocean wash this blood Clean from my hand? No; this my hand will rather The multitudinous seas incarnadine, Making the green one red. Duke Felmet washes his hand with increasing vigour and increasingly rough tools until it no longer resembles a hand.
He bemuses Death by acting like a ghost when not yet dead. Asked why he's still here, Death calmly replies, "WAITING" . At that point, in a deeply-satisfactory-to-the-reader fashion, Felmet falls from the battlements. His venom is still not entirely abated however: he vows to stay around and 'make basket chairs creak alarmingly at nights.