Pong - Atari (and all of video games)

Founder Nolan Bushnell created the arcade game Computer Space in 1971, but it had niche success at best.  He and his partner hired Al Alcorn in 1972, their first real employee.  As a training exercise, Nolan asked Al to make a Tennis game.  Al came back with the game Pong.  He did such a good job on the game, they decided to put a machine in a local bar to see how people would like it.  The next day someone called Atari and complained the game had stopped working.  When they investigated they found that the machine was overstuffed with quarters.  After taking out all of the quarters, the game worked fine again.  The video game industry was now born.  The rest is history.

A lot of you aren't really mentioning games that saved a company from certain doom if the game didn't happen though.

I'd mention Donkey Kong (arcade) by Nintendo. Nintendo's first arcade game was a bust, and Donkey Kong was a last ditch effort which happened to become huge. Nintendo could've still been an unknown playing card maker to this day, or could've not existed anymore at all.

Nier automata

Street fighter V, although mainly because Sony paid for exclusive publishing.