The leading antagonist in the episode "Space Seed" of Star Trek: The Original Series. Spawned the second Star Trek movie, titled "The Wrath of Khan". Khan was the leader of the genetically engineered "super humans" created during the fictional Eugenics
War (World
War III), which occured in the late 20th century.
Kirk's famous outburst in the movie, in which he screams, "KHAAAAAAAAN!" is still used today to express rage at a situation.