When it comes to huge rivalries in Star Trek, you've got a lot to choose from. There's Picard vs. the Borg/The Borg Queen, Janeway vs. the Borg/The Borg Queen, Quark vs. unions, and of course there's Sisko vs. Dukat. Though nothing in Trek really touches that last one, but when it comes to the classic crew, who can forget James T. Kirk vs. Khan Noonien Singh?
The original Star Trek Season 1 episode "Space Seed" introduces Ricardo Montalban as this exiled Napoleon fascist who attempts to conquer the Enterprise. He fails, and Kirk sends him and his crew off to Ceti Alpha V. That seemed to be the end of it, until Star Trek II needed a new story and producer Harve Bennett started watching classic episodes. Khan stuck out instantly as being a character that could give the sequel something that Star Trek: The Motion Picture did not have — a villain. Sorry V'Ger, but you've got nothing on Khan. Or unions, if you're asking Quark.
Khan is full of vengeance in the film that would eventually be titled Star Trek II: The Wrath of Khan, but in "Space Seed" he's a misunderstood legend with an extremely warped view of existence. A genetically enhanced intellect does not prevent references to a "master race" escaping his mouth, and he is definitely the hero of his own story. This is in the writing of the episode, no question, but a big reason that it works so well is because of Montalban's performance.
Montalban makes Khan iconic, so much so that the drama is ramped up even more in the film that bears his name. It's rare that the events of any original series episode got a follow-up, their self-contained, one-and-done nature was a part of the series' DNA. "Apollo" never returns and no one has another visit with the Guardian of Forever. In books, maybe, but not on screen.
Khan was an exception. "Space Seed" is a classic that begged for it's storyline to continue, and continue it did.
Welcome back to Warp Factor, where we're exploring "Space Seed" and the notorious Khan. From the battle-stricken 1990's (which I'm sure we all remember) to Strangelock Khanbersmaug making a surprise entrance (kind of) in Star Trek: Into Darkness, we're going 'round the Moons of Nibia and 'round the Antares Maelstrom and 'round perdition's flames with this one. Lock phasers, get the camera off of Chekhov, change Marla McGivers' hair, and enter the prefix code... it's all we've got.