Acting for Two: Laurence Luckinbill plays both Sybok and "God" once the entity assumes Sybok's appearance, leading to a very affecting scene where the (essentially) good-natured and now disheartened Sybok is facing off against his mirror image, who is actually a sadistic and powerful energy being that is ready to murder the Enterprise crew if they don't do what he wants.
Actor-Inspired Heroism: William Shatner's original draft included McCoy and Spock betraying Kirk along with the rest of the crew. However, DeForest Kelley and Leonard Nimoy flat-out refused, pointing out that it would be out of character for either of them, Spock especially, given how Kirk gave up everything to resurrect a Vulcan whose honored last words included "I have been and always shall be your friend".
Cast the Runner-Up: William Shatner originally intended George Murdock to play the Klingon diplomat Korrd, but changed his mind on seeing Charles Cooper's performance. Murdock was recast as the "God" entity.
While Gene Roddenberry didn't like the post-Motion Picture Trek films, he really didn't like this one, saying it was "Apocryphal, at best" and mandating that TNG writers ignore it (a directive they were mostly happy to heed). Several of the cast and crew also have low opinions of the movie.
Though most of the cast and crew have admitted they enjoyed working with William Shatner because of the level of energy he brought as director, others have been less kind.
Shatner later admitted that the revelation of Sybok being Spock's half-brother was like something out of a soap opera. The twist was added as a justification for Spock betraying Kirk, but when that was dropped, it just felt unnecessary.
Creator Cameo: Producer and co-writer Harve Bennett, having had voice cameos in the three previous films, finally appears on-screen as Admiral Bob.
Despite having a long history as a successful TV producer and being one of the two men — the other being Nicholas Meyer — who saved the Trek franchise with the second movie, producer Harve Bennett's career was utterly ruined in part by the failure of this movie. Afterwards, he wanted to do an "origin" story with the older characters as a framework, but Paramount wanted a big 25th-anniversary celebratory movie instead, and when after initially green-lighting his idea they then reneged, he gave up and quit the company. Unfortunately, this film's underwhelming box-office performance and critical drubbing made it virtually impossible for him to find employment elsewhere for the rest of his life, and his only other major work afterwards was on Time Trax.
William Shatner's career ultimately survived The Final Frontier, although obviously any hope he had of becoming a major director went up in smoke afterwards.
The acting career of Cynthia Gouw (Caithlin Dar) didn't exactly take off either. She switched gears and became an Emmy Award-winning journalist.
Effects artist Bran Ferren was at the beginning of a promising career, having previously done effects work for Altered States, The Untouchables and Little Shop of Horrors, but it was his work in this film (see Special Effect Failure) that torpedoed his career as an effects artist in movies. He ultimately ended up having a long career designing theme park attractions for Disney.
The Danza: Harve Bennett's character is Admiral Robert Bennett.
A short scene in which Sybok and his followers ride to Paradise City. Sybok extends his hand, saying "Behold Paradise!"
The scene in which Caithlin Dar first meets St. John Talbot and General Korrd was originally much longer. Talbot asked Dar what terrible crime she's committed to get exiled to Nimbus III, to which she replies that she actually volunteered for the post. Talbot then tries to explain to the idealist Dar that Nimbus III has been a failed experiment from the beginning, while Korrd makes remarks about Romulan women in Klingon language. Demanding translation, Dar learns Korrd wants her to open up her blouse, to which she tells the drunken general "the only Klingon expression she knows", to which Korrd (in English) replies: "Screw you too!" Both Talbot and Dar are surprised that he actually knows English.
The original ending of the scene in which Sulu and Chekov are lost in the woods implied that they are actually at Mount Rushmore National Memorial, to which a fifth President's face (a black woman) has been added. A matte painting of this shot has been created, however it ended up cut from the final film.
Executive Meddling: The original story idea from Shatner involved the Enterprise encountering Satan posing as God, and Kirk and Spock descending into Hell to rescue McCoy ... which probably wouldn't have been suited to Star Trek anyway, really. The executives also demanded "More humor!" (due to the previous film's success in that area). This resulted in severe Mood Whiplash between a grand, epic story about the search for God and slapstick farce. Last, they slashed the film's budget, resulting in awful jokes and massive special effect failure throughout.
The Merch: Along with the usual action figures and plastic models, Kraft offered a 'marshmelon' dispenser.
Off-the-Shelf FX: Kirk's rock climbing shoes were made by Reebok, and he wears a pair of Levi jeans.
Spock's rocket boots are obviously ski boots with rocket nozzles glued on.
Old Shame: Virtually nobody involved with the film has anything good to say about it. William Shatner has since admitted that the film fell short of his vision for it and that it greatly harmed the franchise. Several cast members, among them George Takei, also disliked the final product. The person probably the most positive about the film in retrospect is screenwriter David Loughery, and even he admitted that it could have been better had the writer's strike not cut into the time he had to work on the script.
Real-Life Relative: Bill Shatner's youngest daughter, Melanie, played the Enterprise yeoman.
Recycled Set: Several shots were filmed on sets of the Enterprise-D. TNG was in its 2nd season at the time.
Screwed by the Network: Retroactively. While most of the other TOS-era films were given "Directors Cut" reedits and re-releases, any of which allowed the directors to make improvements — albeit Star Trek III: The Search for Spock has never had any releases aside from its theatrical cut, whereas Star Trek IV: The Voyage Home only got an international cut that added a short pre-title sequence and a couple of other mild changes — William Shatner was famously denied the opportunity to put right this film with a Director's Cut, even though of all six original films, it was the one that needed fixing the most.
Write What You Know: The scene in which McCoy disconnects his father David's life support systems was inspired in part by the death of William Shatner's father. Watching Kelley and David McCoy actor Bill Quinn perform that scene was emotionally difficult for Shatner, who found himself reminded of his father's death in that scene. For his own part Kelley was reluctant to film that scene because he believed some fans would have object to McCoy "pulling the plug" until a line was added where McCoy was asked why he disconnected his father's life support.
Shatner's attempt to direct a Star Trek film led to the movie winning the Worst Picture of 1989 Golden Raspberry Award. He personally won the same "awards" for Worst Director and Worst Actor.
" in the Lower Decks episode "I Have No Bones Yet I Must Flee".