Diablo, an incredibly powerful demon, is the Lord of Terror and one of the Three Prime Evils of Hell, who had been imprisoned in a Soulstone and buried in caverns deep beneath the town of Tristram centuries ago by an ancient people known as the Horadrim. Though his imprisonment was meant to be eternal, Diablo worked tirelessly to corrupt his Soulstone, eventually overpowering his prison. Diablo received help from the thoroughly corrupt Archbishop Lazarus, who had been turned into his loyal servant. However, in order for Diablo to actually manifest himself in the mortal realm, he needed a mortal vessel to house his spirit.