An unsavory and often sneaky character who is in the employ (off the books, of course) of someone with money and possibly some respected position of authority, and carries out certain dirty deeds on their patron's behalf so the patron can maintain plausible deniability in the matter. This character is often found working (secretly) for the Villain with Good Publicity. Compare Psycho Sidekick. Not to be confused with ACTUAL pet rats, such as Scabbers in Harry Potter.
- Alistair Harper and his gang are hired in this capacity by the government when the existing police force isn't enough in V for Vendetta.
- Robert G. Durant and his gang while working for Strack in the 1990 film Darkman.
- The Brute Squad hired by Prince Humperdinck in The Princess Bride. Their job is to clear out the Thieves Quarter.
- And Vizzini and his crew even more so, really.
- The Warden does this to the main character in The Shawshank Redemption.
- Clarence Boddicker from RoboCop (1987) is this for the Big Bad, as he runs errands for him along with his own criminal businesses.
- Beadle from Sweeney Todd, who happens to be played by that other rat. In the story he does a lot of dirty work for Judge Turpin.
- In the Discworld series, competent rulers employ pet rats as a matter of course, though they sometimes find ways to keep them on the books.
- Virtually the entire population of Ankh-Morpork seems to be in this relationship to the Patrician sometimes, though some are a little less rat-like than others. The Dark Clerks and Moist von Lipwig at least maintain fašades of respectability most of the time, while Commander Vimes keeps Nobby Nobbs in the reformed Watch because of his keen feeling for the streets.
- In The Colour of Magic, a more sordid early version of the city has a lot of rat-like figures working unofficially for the government.
- In Jingo, 71-Hour Ahmed is overtly employed as a Klatchian government agent, but his scary demeanour makes people think of him as pet rat when he's really rather more.
- In Carpe Jugulum, the de Magpyr vampire clan employ human guards who seem to have been hand-picked for viciousness.
- In Going Postal, Mr Gryle is Reacher Gilt's killer rat.
- There are quite a few in A Song of Ice and Fire thanks to the feudal nature of the system... although calling "The Mountain That Rides" a "rat" is, frankly, not doing Gregor Clegane justice, for all he does do some seriously dirty jobs for House Lannister beyond simply killing problems as messily as possible. And, then there is the fact that this is the Brave Companions aka "The Bloody Mummers" whole shtick. Lord Walder Frey is a notable example of the breed, though. He's certainly a very slimy rat... who occasionally doesn't even bother to turn up to do his job as a pet and went on to throw in the towel and become a full-on Starscream, but only with the help of more powerful backers. Even when switching masters to gain the new job, he still needs to have one to bolster his own position in the world.
- Harry Potter has Mundungus Fletcher, purveyor of miscellaneous objects of dubious provenance, as Dumbledore's pet rat.
- Michael of Burn Notice is treated like this at times. A burned spy, nobody wants to be caught employing him, so all of his work is strictly off the book. Even when the CIA hires him again Michael is warned that he'll take the fall if an op goes bad.
- In Knickerbocker Holiday, Stuyvesant's first action after his New Era Speech is to secretly hire Tienhoven as his pay-off man. Tienhoven has been illegally selling guns and liquor to the Indians, a business which Stuyvesant intends to make a government monopoly. Concealing such activities will help demonstrate that the government can do no wrong.
- Several of William Shakespeare's plays have lower-class characters who are secretly hired by the Villain Protagonist nobleman to murder his rival(s), most notably Macbeth and Richard III.
- Zipper, Eric Raymond's go-to henchman in Jem and the Holograms
- Truth in Television. Pretty much every country has a department or three of these guys.