Throughout the years, Star Trek has taken various forms. And, be it a television series or film, there have been famous faces that were not a part of the consistent ensemble. This started with Star Trek: The Original Series, which featured recognizable guest stars such as Fred Williamson, Sid Haig, Charles Napier, and Joan Collins.

Then, over a decade after that show wrapped up its brief three-season run, a film franchise kicked off. And, like the original series and The Next Generation (which began between the releases of the fourth and fifth films), there were some big names attached. They may not have always held the spotlight for long in the films, but they were there. So, who's in what? Let's find out, but note that the films subject to inclusion were only the ones that featured either The Original Series cast members or The Next Generation cast members. In other words, no Chris Pine, Benedict Cumberbatch, Idris Elba, or Zoe Saldaña here.

7 Stephen Collins in Star Trek: The Motion Picture (1979)

Like some of the show's most deeply philosophical episodes, Star Trek: The Motion Picture tries to bite off a lot. But, in the case of the movie, it's more than it can chew. Yet, it does feature a former celebrity in a big role: 7th Heaven's Stephen Collins as Willard Decker. Collins' Decker is always butting heads with Captain Kirk, who has suddenly replaced Decker as the captain of the Enterprise.

The Most Controversial Performer on this List

TV fans will recognize Collins not only from the long-running 7th Heaven, but also No Ordinary Family and It's Always Sunny in Philadelphia. As for that latter show, he portrayed the biological father to Dennis and Dee Reynolds. Collins' career ended when he confessed to multiple instances of sexual misconduct against a minor, including once a few years before he nabbed the Star Trek role. Stream Star Trek: The Motion Picture on Max.

6 Kirstie Alley, Paul Winfield, and James Horner in Star Trek II: The Wrath of Khan (1982)

With tight pacing, the franchise's best villain, Star Trek II: The Wrath of Khan is the best Star Trek movie to date. It also features a few familiar faces in The Terminator's Paul Winfield and Cheers' Kirstie Alley. The former plays Clark Terrell, the captain of the Reliant who is subjected to Khan's eel torture, while the latter plays Saavik, a protege to Spock. Not to mention, the late James Horner provided the film's music, but had a cameo role as an Enterprise crew member.

You've Certainly Heard Horner's Work

Widely regarded as one of the cinema industry's great composers, Horner tragically died in a plane crash in 2015. But he left a massive body of very impressive work, and The Wrath of Khan was one of his earliest projects. Throughout his career, Horner was nominated for Academy Awards for Aliens, An American Tail ("Somewhere Out There"), Field of Dreams, Braveheart, Apollo 13, A Beautiful Mind, House of Sand and Fog, and Avatar. He also won both an Oscar and a Grammy for Titanic, the former for the score and the latter for "My Heart Will Go On." Stream Star Trek II: The Wrath of Khan on Max.

5 Christopher Lloyd and Miguel Ferrer in Star Trek III: The Search for Spock (1984)

Star Trek III: The Search for Spock may not be a fan-favorite when it comes to the original run of Star Trek movies, but it's generally viewed in a better light than the fifth film. And, unlike the fifth film, it features several big names on the cast list. These include Back to the Future's Christopher Lloyd and RoboCop's Miguel Ferrer.

Actors Not Unfamiliar with Sci-Fi

Lloyd portrays the main antagonist in the late Leonard Nimoy-directed film, and he impressively sheds most of the likability he possessed in Taxi and would again show two years later in Robert Zemeckis' classic sci-fi film, Back to the Future. His Kruge is a Klingon officer with his sights set on using a terraforming device called Genesis for evil. As for Ferrer, his role was far briefer, as he played a First Officer aboard a fellow Federation ship, the Excelsior. Stream Star Trek III: The Search for Spock on Max.

4 Christopher Plummer, Christian Slater, and Kim Cattrall in Star Trek VI: The Undiscovered Country (1991)

The even-numbered Star Trek films, at least of the original six, are the best. So, until Star Trek: Generations rolled, the intergalactic film franchise left off on a high note with Star Trek VI: The Undiscovered Country. And a big part of that is the inclusion of The Sound of Music and Knives Out legend Christopher Plummer.

Plummer Steals the Show

It's essentially all a Cold War allegory with the Klingons standing in for the Russians. And, while many of the Klingons are ready to strive for peace, there's always someone who sews discontent. That'd be Plummer's general, eye-patch-adorned Chang. But, he's not the only familiar face with considerable runtime, as there's also Sex and the City's Kim Cattrall as the Vulcan Valeris, the ambitious new helmsman of the Enterprise. Not to mention, there's a blink-and-you'll-miss-it cameo from Christian Slater, a fan of the franchise and son of the film's casting director, Mary Jo Slater. Stream Star Trek VI: The Undiscovered Country on Max.

3 Whoopi Goldberg, Malcolm McDowell, and Alan Ruck in Star Trek: Generations (1994)

At one point, Star Trek writers wanted to bring William Shatner's Captain Kirk back, but with a villainous twist. That idea was nixed, but Shatner did find a way back into the universe after the initial film franchise had wrapped up. That said, his reprisal of the role in Star Trek: Generations was more or less to kill him off so the IP could change. But, it had a major similarity to the previous film: a big name in the antagonist role.

McDowell in His Element

In the case of Generations, that would be A Clockwork Orange's Malcolm McDowell as Tolian Soran, who holds the distinction of actually killing William Shatner's Captain Kirk. Ghost's Whoopi Goldberg also appeared as Guinan, a role she inhabited from 1988 to 1993 on Star Trek: The Next Generation. Succession's Alan Ruck also has a substantial role as Enterprise-B captain John Harriman who, like his character on HBO's hit series, comes from a wealthy family. Stream Star Trek: Generations on Max.