Hadriel was a follower of Tyrael. During the awakening of the Prime Evils, a group of heroes pursued Diablo into the Burning Hells. Around this time, Hadriel learnt of Tyrael's involvement with Sanctuary, and of his own volition, entered Hell to aid the heroes in traversing Hell's treacherous pathways.
Hadriel is first seen in Act IV of Diablo II. He is found in the River of Flame, just north of the waypoint, at the edge of the causeway separating the River of Flame from the Chaos Sanctuary. He does not battle against the monsters, as Flavie does in Act I, and is ignored by them in turn.
Hadriel does not share in party-friendly auras, but he gains the effect of party sharing Warcries. This is redundant, however, given his lack of involvement in combat.
Hadriel is clickable, and has two speeches, depending on whether a character has already finished the Hell's Forge quest:
"Proceed, hero, into Terror's Lair. Know that Diablo's innermost sanctum is hidden by five seals. Only by opening each of these seals can you clear your way to the final battle." (after quest completion)
Deckard Cain: "Between the River of Flame and the Archangel Hadriel stands a row of statues, guarding the way to the Chaos Sanctuary. As you pass each statue, take notice as they turn their head and follow you with their icy stares. What purpose could they serve? Perhaps they are the eyes of Diablo himself!"
- To Hell and Back claims that Hadriel was not physically present in Hell, that his appearance was rather a projection.
- Prior to the release of the Lord of Destruction expansion, there were a number of rumors regarding the missing Act IV Hireling. There were many rumors regarding the presence of a hidden Act IV mercenary that could only be hired by completing Hell difficulty - the angel. The angel was supposed to be supported by the presence of Hadriel, who by their conclusions, had obviously no other purpose. The angel was supposed to have Hadriel's base structure, levitated like him and used Cold and Lightning Spells as his main attacks. Ultimately, it was proved false when the expansion was released along with the new Hireling - the Barbarian.
- Hadriel is voiced in-game by Bill Roper, famous for voicing Diablo himself.