From Blizzard's New MMO Wiki
Diablo is a dark fantasy-themed action role-playing game developed by Blizzard North and released by Blizzard Entertainment on January 2, 1997.
Set in the fictional Kingdom of Khanduras, located in the world of Sanctuary, Diablo has the player take control of a lone hero battling to rid the world of Diablo, the Lord of Terror. Beneath the town of Tristram, the player journeys through sixteen dungeon levels, ultimately entering Hell itself in order to face Diablo.
An expansion pack, entitled Diablo: Hellfire, was released in 1997, although it was not created by Blizzard Entertainment. This was followed by a sequel, Diablo II, in 2000, and a third game, Diablo III, was announced on June 28, 2008, at Blizzard's World Wide Invitational in Paris, France.