William Shatner says he was initially against the idea of revisiting Khan for Star Trek II. That's an odd thing to reveal, since when fans think of the quintessential Star Trek villain, the character that likely comes to mind is Khan, who clashed with the crew of the Enterprise in both the original series and Star Trek II. However, if it was up to Shatner, the movie would have featured a completely new antagonist.
Khan Noonien Singh first appeared in the season 1 episode 'Space Seed' as a villain, played by Mexican actor Ricardo Montalban. Montalban reprised the role in Wrath of Khan, which was the sequel to Star Trek's first feature film, Star Trek: The Motion Picture. Directed by Nicholas Meyer, The Wrath of Khan was well-received by critics and fans alike. Decades later, the character was chosen to be the antagonist in the 2013 film Star Trek Into Darkness, the second movie in the reboot of the franchise. This time, the character was played by Doctor Strange star Benedict Cumberbatch.
Shatner revealed in an interview with IGN that during early discussions for Star Trek II, he was opposed to the idea of bringing Khan back for the sequel, simply because he was an established character from the series.
"And I kept saying, ‘Why do we want to go to a segment? Why don’t we invent something absolutely new?’ And the people in charge were much more aware than I was that the fans would be more sympathetic to… [it] would be a better vibration if it echoed a popular hour from the series, and make that, and then further the story as a film."
Shatner admits now that the filmmakers were "absolutely right" in making Khan the villain. The actor says the movie benefited from having Montalban play the character, and says that Khan being a powerful villain made him a good fit for the movie, as it makes the hero appear stronger when overcoming such a powerful adversary.
Khan was introduced in 'Space Seed' as a conqueror, and the leader of a group of genetically engineered superhumans. He and his people were frozen in suspended animation when discovered and awakened by the crew of the Enterprise. After a failed attempt to take the ship, Kirk sentenced him to exile. Khan returned to seek revenge in Star Trek II. It's been reported that Meyer, the film's director, is developing a TV series that will focus on the events that took place during Khan's exile.