Merlan le Dyable
'Merlan the Devil'
Marian le Semble, Marlant lo Simple, Merlan le Simple, Merlant le Dyable, - le Simple
In earlier life called Merlan le Simple, he acquired the sobriquet "le dyable" ('the devil') after his coronation because he turned out to be a real rotter, cruel and treacherous. He hanged his own father on an oak in the forest.
He was eventually killed when he insisted on fighting Lancelot before granting him hospitality in his pavilion. Although Lancelot only learned it after killing the petty monarch, he had done the country a good turn.