Baal, the Lord of Destruction

Baal was the most brash and reckless of the Prime Evils. After the Dark Exile, he was contained within the Horadrim Tal Rasha and entombed. Centuries later, Diablo freed Baal, who then corrupted the Worldstone to devastating effect for the barbarians who lived near Mount Arreat. The heroes killed Baal shortly afterwards. -- Deckard Cain