In the Blu-ray special feature "The Captain's Log", Ricardo Montalban says that once he committed to this film, he realized that he had trouble getting back into the character Khan. After years of playing Mr. Roarke on Fantasy Island (1977), he found that he was "stuck" in that character. He requested a tape of Space Seed (1967) from Paramount Studios, and proceeded to watch it repeatedly. By the third or fourth watching, he had recaptured the essence of Khan's character.
Several episodes of Star Trek (1973) had revisited previous episodes of Patrouille du cosmos (1966), and this inspired the makers to produce a movie that would be a follow-up to a Star Trek (1966) episode. Producer Harve Bennett viewed all 79 episodes, and chose Space Seed (1967) as the best candidate for a sequel; Spock even remarks at the end that it would be interesting to return in a hundred years or so to see what type of civilization had grown there. This is the first time a feature film was made as a sequel to a specific television series episode.
The famous "Space, the final frontier" monologue is heard for the first time since Patrouille du cosmos (1966), now narrated by Leonard Nimoy, however this has been changed slightly. Instead of saying, "...its five-year mission..." and "to seek out new life," this now says, "her ongoing mission..." and "to seek out new lifeforms".
Producers went ahead with a movie script featuring Khan, taking it for granted that Ricardo Montalban would be interested in or available for this film. Specifically, it was overlooked that Montalban at the time was busy starring on Fantasy Island (1977). Montalban was receptive when approached about reprising the role, and arrangements were made to film the movie so as not to conflict with Montalban's "Fantasy Island" scheduling.
One of Admiral Kirk's antiques is a Commodore PET computer.
James Horner: running down a corridor during the preparation for the final battle, just before the torpedoes are loaded into the launch bay.