Originally developed by Synergistic Software and released in 1997, Hellfire was not an official Blizzard product and did not carry Blizzard’s endorsement or label. Despite that, in response to Diablo players who have expressed a desire to experience the content, Blizzard has given the OK for it to be included as a free add-on with Diablo purchases on GOG.COM.

Hellfire offers a non-canonical single-player storyline where players must defeat a powerful demon named Na-Krul who is threatening Tristram. The expansion also adds a Monk class, new weapons and items, new missions, locations, dungeons, and enemies. Hellfire will be accessible while launching the original Diablo.