No real insight into his background is ever given in the game.
His name is a portmanteau of Beelzebub, one of the Seven Princes of Hell in catholic Biblical lore and Baal, the Canaanite deity mentioned in the Hebrew Bible as the primary god of the Phoenicians.
After Lord Mortimer turns on Bathory and Tepes and kills them, Beezelbaal points out to him that he is in violation of their contract. After which he leaves in a puff of flame. Beezlebaal is the only member of Gore Quaffer to survive the game.
Beelzebaal will only be fought once in the entire game. He will be found inside the Gor Castle. He summons demon imps and fire in the fight against him. He will fly later on in the stage which will make hitting him slightly more difficult. Since he is a main boss, he cannot be finished off.