Duriel

Duriel is one of the four Lesser Evils and the act boss of the second act of Diablo II: Lord of Destruction. Duriel, Prince of Pain: Once allied with Azmodan and Belial when they overthrew the Prime Evils, Duriel aided Diablo in finding the Tomb of Tal Rasha in the deserts of Aranoch, where Baal was imprisoned. Once Diablo freed Tal Rasha/Baal, Duriel remained in the tomb to confront the adventurer searching for it. Duriel was defeated by the adventurer. When the adventurer enters in the Tal Rasha's chamber Duriel says "Looking for Baal?"

Notes:

 * Duriel might be related to the Mistress of Pain from Diablo III.
 * Duriel has a slight resemblance to StarCraft's Hydralisk and Lurker
 * Duriel has a unique item named after him, Duriel's shell, a Cuirass: It is possible that, being an insect-type demon, it is his molted shell and not his real carapace.
 * Despite Duriel's Aura being the Paladin's Holy Freeze, it has been said to be of a demonic nature.