Between the Tholians, another Doomsday Machine, more Tribbles, the Talosians, when the topic of an antagonist for the first Star Trek movie came up and was read, surely someone realized that this villian is damn near the same thing as Nomad from the classic episode "The Changeling" except on the big screen. When the time came for a second movie, the writers and creators went to the well of TV characters for villians again. Khan was undoubtably a loose thread that damn near conquered Kirk and the rest of the crew in his episode "Space Seed" but he was not killed, only exiled. Rather then make a "Super Khan" for the BIG SCREEN, they got Khan and nobody will ever forget how good a choice that was.
Once you see him in Star Trek II, Khan is at the top of all conversation that or in some relation to what he is doing. Whether it be the crippling damage he does to the Enterprise, his want of the Genesis device, dead crew members and even a little bit of Kirk's talk about his life as he converses with a lost love about "A man I haven't seen in 15 years is trying to kill me. You show him my son and he'd be happy to help." After spending 15 years trapped on a remote planet with a hostile environment, seeing his comrades die and his wife perish he only saw one man to blame. Not himself for leading his men and facing the consequences of his actions time and again, his superior ego and intellect wouldn't allow that, no he blames Kirk. Kirk left him on the planet. Kirk never followed up on how well Khan's progress was, Kirk could have relocated them if he did find them and maybe his wife would still be alive. Kirk didn't do any of that, and now Kirk must die.
Khan as an antagonist in the movie or the classic episode he appeared in was great. He wants power. In this show, it's possession of Kirk's Starship so that his people can be free and attempt to conquer the galaxy. In the movie, it's something similar, the Genesis device, a creation that Khan will indeed pervert into a deadly weapon and again, conquer the galaxy. You don't see his point or politics, you don't see his angle or sympathize with him. He is as evil a man as they came.
What became a sad case with the Trek movies, (especially the TNG ones) is that they kept wanting to get bigger and better villians to be larger then life then Khan. Wanting bigger weapons and be even more outlandish. Khan succeeded where many of them fell since you knew where he came from, you knew what hurt him and when he is defeated in a cat and mouse shoot out, you only get to savor a win for so long before more of his revenge is enacted.
When the movie is over, do this. Think about Kirk, his career and life and what comes ahead for him and the rest of the crew. Theres a void that cannot be filled and had the ending not been altered by the next movie, whenever Kirk thinks of his best friend he will think of the man that was responsible.
