Doom

From Unidoom Wiki

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Released in 1993, Doom is the first major breakthrough in first person shooters, raising the bar and setting the standard for both single player and multiplayer gaming.
It has spawned hundreds of imitators, few of which have ever recaptured the speed or balance of Doom's gameplay.

Except for maybe Doom 2.

Doom is to UniDoom as Earth is to humanity.