DOOM

DOOM defined first-person shooting and opened the door to networked competitive play (deathmatch) and mod culture. On the origin of deathmatch, an academic book records Romero's remark that playing Japanese fighting games — Street Fighter II among them — inside id's studio fueled the idea (the original interview's publication is still being identified, so this line is drawn as an established account). Distribution was an invention too. They gave away Episode 1 for free, told vendors "sell it for under nine dollars and keep all the profit," and sold the full game direct. In Taiwan, they sold legitimate copies to pirate vendors at a low price, effectively legitimizing the piracy itself — "to us, that was distribution" (Romero, 2026). Carmack designed the engine and levels as separate from the start, and WAD files let anyone modify the game. Counter-Strike would later emerge through this door.