1. Spacewar! (1961)
Programmed by Steve Russell in 1961, Spacewar! pitted two players against each other, each controlling a tiny ship that spun around a gravity well in the center of the screen. Both ships had limited ammo and fuel, as well as a "hyperspace" ability that could be used as a last-ditch attempt to avoid an enemy's shot--pretty complex for a game running on a computer only marginally more powerful than a sun dial.
What, you haven't played Spacewar!? That's fine, we won't hold it against you. It's not like you have a Programmed Data Processor-1 computer sitting in your basement or anything. But despite being relatively unknown in 2013, it's unarguably significant to the history of video games for one, important reason: It's the very first one to gain any semblance of popularity. Like, ever. Spacewar! wasn't a replica of a real-world sport, either--it was its own thing, and that originality inspired development of future games like Computer Space, Tank, and Combat. It laid the foundation for our industry, and earns its place as the most important game ever made. Though there were some experimental game-type-things before it, Spacewar! is the one that's most directly related to the foundation of the game industry.
Looking to the future
Are there other games incredibly important to the video game industry's colorful history? Absolutely. But these are the 50 that we feel are the most impactful. What games would you include on your list, and why? Let us know in the comments below.