Hellfire is an expansion pack that Sierra On-Line (now known as Sierra Entertainment) produced for the computer game Diablo. It was released in 1997 and developed by Synergistic Software, a Sierra division.

Hellfire's storyline occurs as an aside to the main story arc of the original game. It concerns the powerful demon, Na-Krul. The expansion pack adds an additional monk class, two new dungeon tilesets, additional quests, several extra game items, noticeable buffing to Diablo, and a number of interface improvements. Two additional characters -- the bard and the barbarian -- can be enabled with a special text-file edit in your Hellfire installation directory. As test characters, these warriors have new skills & attributes, but do not have unique character graphics developed for them.

Hellfire was the only official expansion pack released for Diablo.