5. Race and Chase's angry AI cops spawned Grand Theft Auto
Before Grand Theft Auto, there was Race and Chase. DMA Design's open-world racer would let you play as either a cop or a criminal and… I don't know, race around? It doesn't matter--according to the developers, it wasn't very fun. It crashed all the time, and the "living world" changed how people played, making for a much less interesting game than DMA intended to develop. Then something broke, and everything fell together.
GTA designer Gary Penn described it in an interview, saying "One day, I think it was a bug, the police suddenly became mental and aggressive. It was because they were trying to drive through you. Their route finding was screwed I think, and that was an awesome moment, because suddenly the real drama was, "Oh my God, the police are psycho--they're trying to ram me off the road." Turned out, being chased by aggressive cops was fun. Who knew?! This realization refocused Race and Chase, and led to the creation of gaming's biggest open-world franchise.