Diablo is the Lord of Terror and final boss in Act IV in classic Diablo II. He is found in the Chaos Sanctuary, where he can only be reached after the player has opened five seals. Three of these seals release a Super Unique and his minions. The player must defeat these minions, and when the last of these monsters fall, all other monsters in the Sanctuary instantly die and Diablo appears atop the central pentagram. If the expansion pack isn't installed, the game ends after 90 seconds following Diablo's death. In Lord of Destruction this does not happen.
Diablo is voiced by Bill Roper, who also did the voice for Hadriel in Diablo II and Ogden in Diablo I.
Diablo is one of the most dangerous monsters in the game. Though the power balance between bosses and regular monsters greatly shifts in Hell difficulty, he is probably the hardest monster for a player to overcome on Normal difficulty, barring Duriel against certain builds.
Like his two brothers, Mephisto and Baal, Diablo comes with an arsenal of various attacks that he unleashes upon the player:
- Bone Prison: Identical to the Necromancer skill. Diablo will use this on Town Portals summoned too close to him, trapping unsuspecting players when they return from town.
- Charge: Allows Diablo to sprint forward quickly on all four. Though it shares names with the Paladin skill, it doesn't deal any damage and doesn't produce the same blurring effect.
- Cold Touch: A melee attack that freezes the player.
- Firestorm: Similar to the Druid's skill, but much larger and longer.
- Fire Nova: Releases a ring of expanding flame that will envelop several screens.
- Fire Wall: Identical to the Sorceress skill.
- Red Lightning Hose: Also known as Lightning Inferno, this skill is without a doubt his deadliest. It works just like the Sorceress' Inferno, but has a longer reach and deals far more damage. Characters with inadequate resists and sub-par gear perish within seconds.
Excluding twinked characters who can simply run up and start swinging, Diablo requires the player to be very mobile. He often uses his Red Lightning Hose attack, and when he does, the player's health will quickly start to deteriorate. At this point it is imporant to immediately stop attacking and start running to avoid it. His other attacks, mainly Firestorm and Fire Nova, deal quite a bit of damage as well, but the former is static and only requires a small sidestep to avoid, and the latter cannot be avoided in any case. Diablo's casting animation for Fire Nova is also quite long compared to his other skills, which allows for plenty of warning to drink a potion and to run away if the situation calls for it.