Complex sentence: According to the backstory revealed in the episode, Khan is one of a group of genetically engineered super-humans, bred to be free of the usual human mental and physical limitations, who were removed from power after the Eugenics Wars of the 1990s.
Split into simpler sentences: According to the backstory revealed in the episode, Khan is one of a group of genetically engineered humans, bred to be superior in physical and mental ability. Some rose to power, as did Khan, but were removed from power after the Eugenics Wars of the 1990s.