If Mario had never been invented, I'd say Pac-Man would be the most recognizable character ever. So, had Shigeru Miyamoto never created Donkey Kong, there would be no SMB, and, as a result, the modern platformer would be vastly different, or even nonexistant. There would be no Mario Kart, which spawned trillions of other "little kids'" racing games, meaning modern racing games would be relegated to more serious series like Gran Turismo. Man, the world would be a terrible place without Mario Party 91/2.
That gets me thinking...What if there was never a World War II, like in Resistance? WWII served as the inspiration for countless WWII movies, which, in turned, inspired programmer Silas Warner to create Castle Wolfenstein for the Apple II, meaning no CW. Since that was the inspiration for Wolfenstein 3D, the first modern first-person shooter, that means, no Doom, no Quake, and no Half-Life.