What inspired Diablo?

Diablo's creator told the whole story himself. In his GDC 2016 postmortem, reported in full by Game Developer, David Brevik explained that he conceived the game in high school and named it for Mt. Diablo, the peak near his Bay Area home: the mountain he grew up under became the mouth of hell.

The design document he wrote at his company Condor described a turn-based, single-player DOS game with roguelike permadeath, in the direct line of Rogue and NetHack, and expansion disks imagined like Magic: The Gathering booster packs. Its world even had a literal foundation stone: the isometric grid was traced from an X-COM screenshot. "The actual tile-square basis, the same shape and size, is exactly the same in X-Com and Diablo."

The planned look was just as specific: stop-motion clay, in the manner of the arcade fighter Primal Rage, whose look Brevik loved. The near-misses, the turn-based heart, the clay skin, and the real-time vote that overturned both, are the next page in this Library. What matters here is the recipe: a roguelike's soul, a card game's expansion model, another game's floor tiles, and a mountain's name.