Cylon

150,000 years ago, the survivors of a bloody war between humans and their mechanical creations, the Cylons, settled on a distant planet where humanity had spontaneously re-evolved. Together with the indigenous, pre-technology humans, they populated this new world, naming it Earth. While memories of their pre-history diminished over time, humanity grew and prospered on Earth.
Eventually, advancements in technology led to the creation of artificial intelligence and robotic bodies.
Upon combining these two, Cylons were re-invented and the fate of the planet determined.