Majel Barrett Roddenberry (23 February 1932 – 18 December 2008; age 76) was a recurring actress in the Star Trek franchise and was the wife of Star Trek creator Gene Roddenberry. Her most frequent portrayal in Star Trek, besides the computer, was that of Christine Chapel on Star Trek: The Original Series, Star Trek: The Animated Series, and in two of the films. She also voiced M'Ress and several other characters on The Animated Series and later played Betazoid Ambassador Lwaxana Troi on Star Trek: The Next Generation and Star Trek: Deep Space Nine. Her first filmed appearance was in the original Star Trek pilot episode "The Cage" as Number One in 1964. link
Jeffrey Alan Combs (born 9 September 1954; age 70) is an actor who has the distinction of portraying nine different characters on four Star Trek television series link
Vaughn Dale Armstrong, Jr. (born 7 July 1950; age 74) is a veteran Star Trek actor who is noted for portraying twelve separate characters in twenty-eight episodes over four separate series. link
In 2011, the Guinness Book of World Records recognized Bill Blair as the record holder in the category of "The Most Special Effect Make-Up Characters Portrayed in a Career" with 202 different characters.
Well that's pretty neat!
That said, I'm not sure uncredited non-speaking roles are really comparable to guest-starring roles.
Fair is fair. If we're talking speaking roles, then after Vaughn Armstrong, it comes down to an 8-way tie between John K. Shull, Paul S. Eckstein, Joseph Ruskin, Thomas Kopache, Paul Boehmer, Randy Oglesby, J.G. Hertzler, and the man himself Combs. Most appearances in general still belongs to Our Man Dorn.
No worries. I've been sitting on that bit of info for a spell and uncertain of how to express it. So, if nothing else, thank you for knocking that one loose! And I've just come up with a way to make that trivia its own meme.
More than just an actress. Majel is the one who encouraged Gene to pitch Star Trek to producers after suggesting some changes to his original idea. She’s one of the reasons the show existed at all.
Her last role in Star Trek was the voice of the computer in the 2009 reboot movie. Unfortunately, she died before it was released.