Diablo is the final boss beneath Tristram in the original Diablo.
The game follows a hero descending through a series of increasingly dangerous levels beneath the cathedral in the town of Tristram. At the bottom, the player confronts Diablo, the Lord of Terror, whose imprisonment beneath the cathedral drives the game’s central story.
Diablo is one of the three Prime Evils, alongside Mephisto and Baal. The original game focuses primarily on Diablo’s return, while later entries broaden the conflict to include all three brothers and their allies. The Butcher is also a memorable enemy from the first game, but he appears much earlier and is not the final boss.
After defeating Diablo, the ending changes according to the hero’s class and actions. The conclusion helped establish the series’ recurring theme that defeating a great evil may carry a serious personal cost.