* DirectedByCastMember: Leonard Nimoy, marking the first time a cast member directed a ''Franchise/StarTrek'' production, paving the way for future cast members like [[Film/StarTrekFirstContact Jonathan]] [[Film/StarTrekInsurrection Frakes]].
** Same can be said for [[Film/StarTrekVTheFinalFrontier Shatner]], but people tend to ignore that one.
** Shatner was, according to "Star Trek Lives," scheduled to direct the final episode of the Original Series in 1969. Unfortunately, that would have been Episode 81, and NBC sent the word down during the filming of "Turnabout Intruder" that that episode, #79, would be the last.
* FakeRussian: In letter, but not in spirit. Chekov actually speaks Russian for the first time. Though Walter Koenig was born in America, his parents are Russian immigrants who emigrated from Lithuania.
* HeyItsThatGuy: [[HillStreetBlues James B. Sikking]] as the Excelsior captain. Also, Phil Morris, who would play [[NoCelebritiesWereHarmed Jackie Chiles]] on ''{{Seinfeld}}'', appears in the beginning as Cadet Foster.
** Not to mention ChristopherLloyd as [[Film/BackToTheFuture "Doc"]] Kruge. His ship even looks like a [=DeLorean=][[note]]It doesn't really[[/note]] . And it was later used for TimeTravel.
** And a post-''Series/BlackSheepSquadron'' pre-''NightCourt'' John Larroquette as the surviving Klingon crewmember.
** "Mr. Adventure" was played by Scott [=McGinnis=], who became a prolific television director.
** I had to kill the ''Excelsior'' helmsman because [[Film/RoboCop1987 he made a mistake]]. Now it's time to ''erase'' that mistake.
* HeyItsThatVoice: FrankWelker did young Spock's screams.
* TheOtherDarrin: Kirstie Alley loved playing Saavik (she apparently wore the ears home a number of times) and wanted to return, but apparently failed to communicate this clearly to her agent, who demanded a higher fee for her to play Saavik than Paramount was willing to pay. Paramount switched in Robin Curtis instead.
* ThrowItIn: Kirk stumbling off the chair after being told [[spoiler:David was murdered]] was entirely accidental, but Leonard Nimoy felt it suited the scene, and left it in.
** To be quite exact: Shatner stumbled on a previous take, whereupon the two convened and decided that the scene should include such a gesture. The recorded take was then staged, leading to the movie we now know.
* WhatCouldHaveBeen: [[Series/BattlestarGalacticaReimagined Edward James Olmos]] was Leonard Nimoy's preference for Kruge.
** Early scripts has the Klingons as a rogue group who commandeered a ''Romulan'' Bird of Prey.
*** And earlier than that, it was supposed to be ''Romulans'', period, in Harve Bennett's treatment. Spock's role is relatively the same, except he goes feral and kills several Romulan miners when they drill for dilithium on the Genesis planet. A subplot would have also had the Vulcans threatening to secede from the Federation over the Genesis Torpedo...
** In the novelization, Saavik and David Marcus became romantically involved (the seeds for this were planted in the [[Film/StarTrekIITheWrathOfKhan previous movie's]] novelization); this storyline was completely dropped from the films.
** In the novelization, Saavik became pregnant with Spock's kid. This, too, was dropped.