In an attempt to keep the Lords of the Burning Hells from taking over Sanctuary, the Archangel Tyrael captured the three prime evils: Mephisto, Lord of Hatred; Baal, Lord of Destruction; and Diablo, Lord of Terror. The prime evils remained imprisoned until Diablo, through contacts with mortals living in the town above him (Tristram), began bringing minions from Hell into Sanctuary. While a hero managed to slay him, the hero soon transformed into a new host body for Diablo's soul. With Diablo setting about in his new host to free his brothers, a band of heroes went after him, managing to slay all three prime evils. In the process, the Worldstone, designed to keep Sanctuary hidden from the High Heavens and the Burning Hells, was destroyed.