Which company developed the original Diablo video game?

Blizzard North developed the original Diablo video game.

The studio began as Condor, an independent game developer founded by Max Schaefer, Erich Schaefer, and David Brevik. Condor worked with Blizzard Entertainment on Diablo, and Blizzard acquired the studio during development in 1996. It was then renamed Blizzard North and became closely associated with the Diablo series.

The game was released for Windows in December 1996 and established the dark action role-playing formula that later Diablo games expanded. Blizzard North also developed Diablo II and its expansion, Lord of Destruction.

A common mix-up is naming Blizzard Entertainment as the developer. Blizzard Entertainment published and supported the game, but the original game's development was handled by its Northern California studio, Blizzard North. The studio was closed in 2005, after which later Diablo development moved to other Blizzard teams.