It was, originally but NBC told Roddenberry to shoot a different one 'cause “The Cage” was “too intellectual.” They didn’t like a woman being the second officer either.
…and unless I’m mistaken that second officer was Majel Barrett Roddenberry, Gene’s wife, who would later on become Dr. McCoy’s assistant, the voice of the Enterprise computers, and Deanna Troi’s mother in TNG! And now we’re back on the original topic 
Melvin Belli was on TOS, once.
Iggy Pop was on DS9 as a Vorta.
I read that Tom Hanks is a MAJOR trekkie, and it would be fun to see him in Enterprise, but that wont happen. Supposedly Robin Williams wanted to do a Trek too, but did not happen.
Trek is really for B actors only.
SP
Mick Fleetwood was on TNG.
Leonard Nimoy’s subsequent directing career (3 Men and a Baby, Funny About Love) probably qualify him as the winner, but I hated both of those movies, so I’ll go with Ashley Judd.
F Murray Abraham was a villian in one of the later movies. He was also an Oscar winner by the time he did his stint.
John Larouquette was in Search for Spock which came out in 1984, the same year Night Court started.
In SOS he plays Maltz, the Klingon who is tricked by Kirk into beaming him onto the Klingon ship.
SOS should be SFS=Search for Spock, obviously.
The unlikeliest guest star was probably tennis player Vijay Amritraj, as a Federation captain in The Voyage Home. But I’m not aware that he went on to a film career …
Well, DS9 didn’t spawn too many huge acting careers from bit part characters, but it did bring in a bunch of fairly well-known older actors for bit parts…
Brian Keith
Frank Langella
Wallace Shawn
Billy Mumy
Louise Fletcher
Tracy Scoggins
Andrea Martin
Meg Foster
Vanessa Williams
Cecily Adams :dubious:
James Darren
Adrienne Barbeau
Oh, and Kim Cattrall was in Big Trouble in Little China before she made Star Trek: The Undiscovered Country.
Kim Cattrall was also in (wait for it)…
Porky’s (1981)
He’s been in a Bond movie too (and they worked in a tennis-racquet gag). But isn’t he bigger in Bollywood than Western movies?
Does Kim Darby count?
She was Miri in TOS.
Kim (Miri) Darby later starred in True Grit and a solid list of films and TV, though she had been a frequent TV guest star before Star Trek.
William Marshall (Dr. Daystrom in “The Ultimate Computer”) reached movie stardom (such as it was) playing Blacula.
Barbara Babcock was in “Plato’s Stepchildren”; she later won an Emmy as Grace Gardner in Hill Street Blues.
Yvonne Craig was in “Whom Gods Destroy” a year before becoming a star as Batgirl.
Fred Williamson had a bit part in “The Cloud Minders,” and then went on to be a big star in Blaxploitation films (as well as in the film MAS*H.
Ah, the IMDB. 