A show or movie where the main cast also serve as the main writers of the piece: essentially, Written by Cast Member and/or Descended Creator taken to its logical conclusion (or, at least, the logical conclusion just short of Copiously Credited Creator).
Common in Sketch Comedy, as well as any independent works on the internet such as Video Review Shows and Internet Abridged Series due to their one-man-show nature. The trope can crop up in other types of show as well; it's especially common in Sit Coms, as sitcom writers often have backgrounds in performance (specifically stand-up and/or sketch comedy) and are susceptible to being called upon to act.
Examples:
- Matt Damon & Ben Affleck's Good Will Hunting.
- Many of the Judd Apatow-produced films and TV shows, and not just because his films are heavily improvised. Steve Carell co-wrote The 40-Year-Old Virgin and Jason Segel co-wrote Forgetting Sarah Marshall.
- Casino Royale (1967) falls into this category - largely because the actual script was such a mess that producers had to get the cast (who included experience writers such as John Huston, Orson Welles and Woody Allen) to try and make some sense of it. Peter Sellers, the nominal star, also wrote a lot of his own material.
- In MAD's parody of Animal House, when Dean Wormer threatens the Deltas, one remarks they have more power than he does because some of them are writers of the movie.
- The original Ghostbusters duology was written by Dan Aykroyd and Harold Ramis.
- The Monty Python team wrote and starred in their movies.
- Series creator Rob McElhenney, co-developer Glenn Howerton, and writer Charlie Day all have lead roles on It's Always Sunny in Philadelphia. Another co-writer, David Hornsby, plays recurring character Rickety Cricket.
- Mystery Science Theater 3000 cast parts almost entirely out of the production staff, and primarily from the writers, to the extent that almost every bit part ever was played by someone who was employed to do something at Best Brains before they appeared on the show.
- All of the replacement actors for the main characters also came from the crew, chiefly the writing staff. It was that kind of show.
- Svengoolie writes pretty much all his own stuff.
- 30 Rock is a show about writers and producers, where Tina Fey plays her own writer/producer character while writing and producing the show. Scott Adsit (who plays Pete Hornberger) and John Lutz (who plays J. D. Lutz) are also comedy writers.
- A lot of Britcoms are created and written by the star(s), especially ones who come from a stage or stand-up background:
- Fawlty Towers starred and was written by John Cleese and his then-wife Connie Booth.
- The Mighty Boosh is written by its stars, Julian Barratt and Noel Fielding, with additional material from Rich Fulcher.
- Spaced was created and written by its leads, Simon Pegg and Jessica Hynes.
- Ricky Gervais and Stephen Merchant wrote and starred in The Office (UK) and Extras.
- The Office (US) also qualifies, as it includes three writers as cast members (Toby, Kelly, and Ryan), and two others have had smaller cameos. Steve Carell has also written episodes.
- Steve Smith, who portrayed the title character of The Red Green Show, also co-wrote every episode. He often worked with Rick Green (who played Bill), and in later seasons, Peter Wildman (Buzz Sherwood) and Bob Bainborough (Dalton) contributed as well.
- Laura Dern and Mike White created and starred in Enlightened, with White writing every episode.
- The League of Gentlemen has its writing credit read "The Cast and Jeremy Dyson", and it's roughly that literal—beyond crowd scenes, children, and the occasional woman, you'd be hard-pressed to find a single character not played by series writers Mark Gatiss, Steve Pemberton or Reece Shearsmith.
- Monty Python's Flying Circus was "Conceived, Written and Performed by" Graham Chapman, John Cleese, Eric Idle, Terry Jones, and Michael Palin. (Terry Gilliam was added to the list in the second series.)
- Saturday Night Live, particularly in the first five years (1975-1980) due to the relatively small cast (and especially in the 1979-1980 season, when Lorne Michaels was looking for replacement actors for Dan Aykroyd and John Belushi, who left after season four), though the tradition of having SNL writers as either cast members or bit players continues to this day.
- The Kids in the Hall
- SCTV
- Second City, The Groundlings, and other Improv troupes generally.
- The State
- The Goodies: two of the three main performers wrote it.
- At Last the 1948 Show: four of the five main performers wrote it.
- That Mitchell and Webb Look
- The Armstrong and Miller Show
- Little Britain
- The Catherine Tate Show
- Almost Live!
- Mr. Show
- Les Luthiers
- Hello Cheeky: three of the four main performers wrote it.
- Radio Active and KYTV were so full of writers that Helen Atkinson-Wood was the only one who didn't chip in on that front.
- I'm Sorry I'll Read That Again, being where all the Goodies and one of the Pythons (John Cleese) started (other Pythons wrote for it but didn't perform). Jo Kendell was also a writer, in particular coming up with the "John and Mary" sketches.
- Pretty much anything on Channel Awesome.
- Many cases on Rooster Teeth.
- Puzzle Clubhouse has a lot of this — it's a series of episodic games created on a fast-paced schedule (a new game releases on the first of each month), and having all the voice actors on site makes for faster iteration and development. The majority of characters are voiced by Schell Games developers (who also write the episodes, design the games, create the artwork, etc).
- The Venture Brothers has a lot of this: writer/creators Jackson Publick and Doc Hammer spend a lot of time talking to themselves; between them they voice something like twelve characters.
- Same thing with South Park, but more so. Trey Parker and Matt Stone voice pretty much anyone who's not Chef or a woman (though Trey Parker voiced Ms. Choksondik, as well as a one-time female character — the S'mores Schnapps lady — in "The Red Badge of Gayness." Mary Kay Bergman was meant to voice her, but had to be replaced following her death).
- Bill Scott, co-creator and head writer of Rocky and Bullwinkle, shouldered the burden of roughly half the lead voice cast, playing Bullwinkle, Mr. Peabody, and Dudley Do-Right, among others.
- Seth MacFarlane, Alex Borstein and Mike Henry both write and perform for Family Guy.
- Jack Mercer wrote for many Popeye cartoons as well as voicing not only the title character but many incidental voices, right through the 1978 Hanna-Barbera series. He did so with many of the Paramount stable. He was also an in-betweener at Paramount.
- Several OK K.O.! Let's Be Heroes characters are voiced by creator and head writer Ian Jones-Quartey. They include Radicles, Darrell, Gregg, Crinkly Wrinkly, and Cookie Man. Likewise, storyboard artist Parker Simmons voices several recurring or one-off characters; his roles include Fish Dude, Gerald Nametag, Skateboard Nerd, Gil Ferris, and Plazamo.
- Mao Mao: Heroes of Pure Heart, created by the aforementioned Parker Simmons, features a main cast primarily comprised of crew members and employees at Titmouse.
- Creator Parker Simmons voices Mao Mao, King Snugglemane, and Ratarang, as well as several minor characters.
- Storyboard artist Griffith Kimmins voices Badgerclops as well as Pinky, Kevin, and Chester.
- Lika Leong, the production manager, voices Adorabat.