Frank Conniff is best known as TV's Frank, Dr. Clayton Forrester's be-spitcurled sidekick on MST3K. Along with his on-screen persona, Frank was also a writer for the show. Frank's duties for the show also included picking a vast majority of the movies featured on the show. Frank also reportedly found many of Coleman Francis' movies hysterical and so they were all featured on the show. Some of Frank's least favorite movies include: End of Days (with Arnold Schwarzenegger), Green Lantern, Sucker Punch and Mamma Mia! 
Currently Frank works as a successful stand up comedian. He produced a long-running live comedy show in Los Angeles called "Cartoon Dump". Frank is also a member of the crew of Cinematic Titanic, riffing on bad movies alongside fellow MST3K alumni.
In 2011, Conniff appeared in the satirical dark comedy God Bless America. Conniff also wrote and performed satirical bits for the second and final season of FX Network's political sketch show "Totally Biased with W. Kamau Bell". Like Michael J. Nelson and Co., Conniff also frequently provides witty comments on his Twitter and FaceBook page.
In a 2012 stand-up comedy act for Top Story! Weekly, Frank revealed that he had been raised Catholic but no longer was of that religion. Instead of being an Atheist, he chose to put his belief in a fictional God. Frank also revealed that he had been sober for 27 years.
In fall of 2014, Frank appeared as the title Frankenstein's monster-based character in the music video comedy short The Frank along with other MST3k members. Later that same year, Frank, Trace and Joel appeared during a short which had them recounting the highlights of their personal experience with Thanksgiving and it was shown in-between the bumpers for Turkey Day '14.
- Gooch - The Sidehackers
- Winky's Mom (voice) - Manhunt in Space
- Tom Servo - The Giant Gila Monster DVD special feature "host segment".
- "I’m from New York City. I’d moved to Minneapolis in 1985 to go into drug rehab. I ended up staying and doing stand-up comedy. Basically, I was a very unknown stand-up comedian when I got on Mystery Science Theater."
- "I’ve never gotten any residuals or royalties from the show, or any money from merchandising. But that has never been a bone of contention with me, because Mystery Science Theater was my first TV show. I’ve always been totally cool with that."
- (on the difference between geeks and nerds) "I think a nerd gets beat up, and a geek gets beat up and then goes and watches an episode of "Buffy the Vampire Slayer." 
- (on his assigned task on selecting the bad movies for the show) "I think I was given the job because everybody else was busy with other stuff. [We looked for] a movie that's really bad but at least watchable and with a somewhat of a plot..." 
- (on his favorite so-bad-it's-good movie) "A movie from the sixties called The Oscar with Steven Boyd and Elke Sommers is my all time favorite bad movie."