[[Image:Mon-Diablo.jpg|frame]]Diablo is the final boss of Act Four, and must be killed to finish the [[Quests_Act_Four#Quest_Three:_Terror.27s_End|Terror's End]] quest; this is the end of the game in Diablo II, and is required to advance to Act Five in the Diablo II Expansion. Diablo appears after all five "seals" and all three seal bosses have been killed in the Chaos Sanctuary.
Like many of the monsters in Diablo II, Diablo was a lot harder in earlier versions of the game. Prior to v1.08, his Firestorm (ground fire) attack could insta-kill virtually any character who took it point blank, since there were so many overlapping pixels of flame at melee range. Maximum fire resistance was essential, along with fire absorption, and digging in for a long toe to toe slug fest with Diablo was almost sure suicide. Hit and run tactics had to be employed, in those days.