- “You lousy bum!”
- ―Muddy's catchphrase
Muddy Mudskipper is a mudskipper (a species of fish capable of crawling out of water and breathing air directly) with the voice and personality of a grizzled vaudeville comedian who hosts an afternoon kids' show.
Muddy is an archetype — the old, jaded comedian who is outstanding at being "on" when on stage but sour and dissatisfied off-stage. There are certain parallels between Muddy and Krusty the Clown from The Simpsons — both have television shows that may or may not be for children, both shower their co-stars with abuse, and behind the scenes they are less than pleasant to be around. He calls everyone he meets "a lousy bum". He also calls Stimpy 'kid.'
Besides being a huge television star, Muddy has dabbled in villainy, at one point kidnapping the Pope (voiced by Frank Zappa) before being foiled by Powdered Toast Man. His name is a parody of Woody Woodpecker. He is voiced by Harris Peet.
The show's theme song (written by John Kricfalusi, Bob Camp & Charlie Brissette) plays up Muddy's particular physical traits:
Who's the greatest mudskipper of them all? Who can skip through the mud with the greatest of ease? What kind of wonderful guy? Who can crawl like a dog without scraping his knees? Who's got seg-ment-ed eyes? It's Muddy Mud-Skipper! It's Muddy! Mud-Skipper! It's the Muddy! Mu-ud Ski-pper show!!!
- In "Stimpy's Big Day/The Big Shot", Muddy is the namesake star of The Muddy Mudskipper Show. After Stimpy's epic ode to Gritty Kitty Litter lands him the co-star slot on the show, the actual cartoon is revealed to be a direct rip-off of Yogi Bear, with Stimpy as Yogi and Muddy as Ranger Smith. Several of Muddy's lines here would also be used as archive recordings for the Nickelodeon 3D Movie Maker.
- In "Powdered Toast Man", Muddy appears as a villain who has kidnapped the Pope.
- In "The Royal Canadian Kilted Yaksmen" several mudskippers with the same character models as Muddy appear during the animal sing along.
- In "Jerry the Bellybutton Elf", Muddy and his wife Mimby attend the party with Ren, Mr. Horse, Bubba, Sven Hoek, Powdered Toastman, The Announcer Salesman, Mrs. Buttloaves and others.
- In "Hard Times for Haggis", Muddy nearly runs over Haggis MacHaggis in his car, but swerves out the way and merely splashes rainwater from a puddle on him. Regardless, Muddy still shouts, "Why don't you look where you're going?! Ya lousy bum!"
- In "Insomniac Ren", Muddy, Mr. Horse and Haggis McHaggis arrive at Ren and Stimpy's place the next morning so Ren can go golfing with them. However, Ren has trouble getting rest, therefore he offers them each five dollars to knock him out literally with their golf clubs. They accept the offer, as well as Stimpy who awakes when he hears this, and they send Ren into a coma. The others then depart to go golfing without him.
- In "My Shiny Friend", Muddy Mudskipper and his own show are referenced on a television. And later, Stimpy, after becoming obsessed with, addicted to and finally overdosing on watching too much television, has a nightmare involving Muddy, who attacks him, then a giant version of Muddy chases him. In another chase scene, giant Muddy is now a huge television with his mouth on the screen (or for the screen) and legs, and the nightmare ends with Stimpy falling into the television's mouth, and being eaten.
- In "Ren Needs Help", Muddy is one of the various patients at a mental institution. He and a yak (possibly one of the yaks from "The Royal Canadian Kilted Yaksmen") are there because the yak claims that Muddy constantly incites and excites him by saying the word "cheese" around him, which sends him into a frenzy each time and he rubs (and eventually wears off) his rear end with a cheese grater.
- In "Dinner Party", Muddy is among the guests at a party in a mansion. Prior to that, he's seen in prison, pulling a lever to a machine that presses license plates. When Stimpy appears and hands him an invitation card, Muddy pulls the lever once again and accidentally presses (and flattens) Stimpy's hand, and arm.
- In "Terminal Stimpy", Muddy may have been killed off for good because his car was struck by Stimpy's and he was gravely injured and asked Stimpy a few favors before passing on, his final request was to be skipped across the road into the pond nearby he ended up being struck by a bus before he could reach the pond, he was last seen stuck to the front of the bus saying "I got another favor to ask you".
- Despite being a Mudskipper, he shares no resemblance to Mudskippers in real life with him being yellow instead of brown and he lacks dorsal fins. He also has teeth, which real life Mudskippers don't have.