Milo Stanley's dog. He is a frequent wearer of the mask as well.

Lt. Mitch Kellaway a lieutenant constantly trying to prove Ipkiss is the Mask. A running gag of the show is that he receives atomic wedgies from the Mask.

Peggy Brandt Stanley's reporter friend. She sold out Stanely to mobsters in the movie, causing their strained relationship, though their friendship was repaired when Peggy rescues him (several times later). She constantly tries to up her career in the tabloids biz usually leaving her in sticky situations. She is one of the many women that The Mask has made advances on.

Doyle Lieutenant Kellaway's dimwitted partner. He is usually the comic relief and is occasionally seen eating a donut.

Charlie Schumacher Stanley's friend in the movie turned into bank manager. He usually looks out for himself, tries to score women, has Stanley do his work for him, etc.

Other characters

Villains
The main villain, Dr. Pretorius (voiced by Tim Curry), was a madman who had his own head removed from his body and placed on tiny, spider-like robotic legs, which could attach to a larger android body. His plans always revolved around either obtaining or controlling the Mask (Pretorius is one of the few characters in the series aware of The Mask's true identity), or as part of some increasingly insane "science experiments" which, if carried out, would result in the death of thousands or even the end of mankind. He mostly pronounces Ipkiss' last name as "Ipp-kiss". Pretorius was also likely a parody of drug dealer/mob boss Eugene Rapaz from the original comics (both share the same face. Rapaz wore small, rounded-lens dark glasses and Pretorius had round optic implants that looked similar, as well).

In the episode, "Sister Mask", Dr. Pretorius did eventually gain the mask, and as with Tyrell, retained his own personality while wearing it (While the mask is said to release one's own inhibitions, those who have no inhibitions seem to retain full conscious control while wearing the Mask, such as the Joker in the DC crossover).

Coming from the comics was Walter, Pretorius's goon, still silent and indestructible but not as murderous and cruel. Walter chased the Mask for several episodes, but when he obtained the wooden mask and it failed to work for him, he simply dropped it. Walter remained a recurring character throughout the series. Walter is strong enough to actually break the Mask in two (an impressive feat as only seconds before the Mask withstood being hit by cars and run over by a steamroller without a scratch).

Ben Stein reprised his role as Dr. Neuman, from the movie. In one episode, the mask falls into Neuman's hands, and he becomes a super-villain. The wacky soul plumber diagnoktiziert now throughout the city Loki Ipkissiamascosus and locks people in cages, because he is with them that mask syndrome looks. He plan determined to kill Stanley and even goes as far as to spring Pretorius from prison to aid him (a running gag, however, was that Dr. Neuman refused to believe the mask worked, even when he had it on).

A third villain who made it to the TV series for a few times was the mad Dr. Amelia Chronos, who, with her ambitions of gaining power and dominance through the manipulation of time, often caused quite a lot of chaos through inventions like a machine that kept looping time every half hour for everyone but herself (so that even the Mask could never foil her plans, since by the time he got to her, everything would be reset to a half hour prior), a gun that reversed/fast forwarded time for whoever it was aimed at (so that the person would keep getting younger and younger until he/she became nothing, or became older and older until he/she was dead), a large time portal through which she could summon anything to defeat the Mask (such as prehistoric creatures, robots from the future, etc) though none of them worked and an actual time machine through which she could travel into the past or future to manipulate events so that she would ultimately be victorious in her quest for world dominance.

Many other villains were introduced, generally DC Comics parodies: Supermask and Super Salad Man (a parody of Superman). Some Marvel references were made however, like The Mask becoming Biclops (a parody of Cyclops), Spiderhyny (alias Spiderman), Green Surfer (alias Silver Surfer) and Toolverine (a parody of Wolverine), and a villain that turned into a dinosaur like Sauron. Notable were Skillit (parody of Mr. Mxyzptlk and Peter Pan, albeit much more malevolent in nature) and Putty Thing (parody of the Batman: The Animated Series version of Clayface, portrayed as a dumb teenager rather than an angry, jaded actor).

The Mask also had a few more villainous enemies in his rogues gallery such as:

Gorgonzola, the Cheese Witch, whose powers include the Cheese-Eye (an eye laser that turns anything into cheese) and the Shot-Cheddar (a razor-sharp cheddar cheese arrow, that would be fired from Gorgonzola's palm). (This character was created as it was the winner of a contest held by Disney Adventures to create a new villain for the series.)

The Tempest: (real name: French Drizzle) A fired weatherman who was struck by lightning which rebounded from a satellite dish onto him and he was mutated into a freak with the ability to control the weather. He put Edge City into a hailstorm and flood. He resembles Robin from Batman: The Animated Series and has powers similar to that of the X-Men Storm. The Mask was able to stop him by opening a manhole which sucked him down, along with the flood waters he created (not to be confused with the Action Man villain with a similar name, origin and powers).

Kablamus: (real name: Joe Blow) A green-haired explosive man who could cause destruction by blowing himself up like a balloon, without dying, but returning to normal size. He has a special pouch in his costume where he puts different grenades that explode with him. Voiced by Jim Cummings.

Channel Surfer: A madman who glides using his surfboard and travels by teleporting through televisions. He had all of Edge City watch the TV shows he liked and he was able to trap Stanley (wearing the mask) inside the television. Was once a man named Raymond Neilsen who went insane after his favorite TV show "Pointy Peaks" (a parody of Twin Peaks) was cancelled due to complaints from viewers. He is a parody of Silver Surfer.

Dragon Lady, War Machine & Rip Tide (a.k.a. The Dark Star Trio): A trio of villains who came out of Doyle's favorite comic book set out to kill Lt. Kellaway after mistaking him as their superhero enemy. The Dragon Lady (Kath Soucie)can transform into a dragon, fly and breathe fire. War Machine (Jim Cummings) is a robot armed with deadly weapons and ammunition. RipTide (Frank Welker) is a punky villain with the ability to transform into water. Stanley/the Mask defeated the trio by ripping the comic book from whence they came. A parody of the Galaxy Trio from the Hanna-Barbera shorts. War Machine appears to be a parody of the Marvel superhero of the same name (although he's a robot instead of a man in a suit), while RipTide is a parody of Hydro-Man.

Skillit: A mischievous imp who hails from the Shadowland, and can use his own living shadow to suck the shadows out of other people, turning them old fast (only the Mask is immune to this) and allowing him to remain forever young (though he is powerless without his shadow). He is over 4000 years old but, in his own words, doesn't look a day over 12 (because of this, when he is captured he is often forced to do homework). He has known everyone who has ever possessed the mask, such as Atilla the Hun, Gengis Khan, and Blackbeard the Pirate. He's played by Jason Marsden.

Chet Bozzack: The high school bully of Stanley who accidentally wore half of the mask when it was cut into two. It is later shown that their Mask sides have something akin to a rivalry. Stanley and Chet along with their half mask personalities battle ended only when Chet stopped his mask personality from killing Stanley. Chet was voiced by Dan Castellaneta.

Putty Thing & Fish Guy (a.k.a. The Terrible Two): (real names: Doc and Eddie) Two comic book-obsessed teenage boys who wanted to be superheroes. Driven by this desire, they went into a nuclear power plant in hopes of obtaining radioactivity. They believed that this state would eventually turn them into comic book superheroes when coming on contact with a bug. They succeeded, but forgot to bring a bug, both became ill and were sent to a hospital. On the way, the ambulance they were on accidentally released them and they crashed into two different stores; Doc in a putty shop and Eddie in an aquarium. This transformed them into Putty Thing and Fish Guy, in the episode "the Terrible Two". Fish Guy envied Putty Thing because he had "the great scorcher super powers" and he didn't. Technically, he was a harmless fish sidekick. Even worse, despite being a fish, he can't swim or breathe underwater. In the episode, "The Good The Bad and Fish Guy", he managed to take The Mask from Stanley and wear it, thus transforming him into Shark Dude, a much more dangerous villain that was much stronger and faster than his previous form, likewise, after Putty thing landed in a tub of radioactive waste he gained the power to shoot explosive laser beams from his mouth, Putty Thing later learns how to shapeshift. The two are likely a parody/homage to Mike Myers' titular Wayne's World character, while Fish Guy resembles Wayne's sidekick Garth Algar (played by Dana Carvey).

Cybermite: A living yet obnoxious computer virus (in a form of a fat termite wearing a leather jacket) who manages to invade and infect Milo's body in Fantashtick Voyage. He grows bigger when ever he eats brain cells and occasionally says some pretty bad jokes. Voiced by Jim Cummings.

Lonnie The Shark: A mobster who has sharp teeth and a hairdo that resembles to a shark's fin. Along with his sidekick Pete (Charlie Adler), Lonnie has his own biker gang that cause chaos within Edge City. They tried to steal the XAW battleship in The Green Marine and attempted to rob a bank in Malled. Lonnie once disguised himself as a "Barney The Dinosaur"-style kids TV host in Baby's Wild Ride. Lonnie was voiced by Glenn Shadix.

Vicky Prat/Davida Steelmine: An illusionist criminal and an old schoolmate of Stanley were she was his crush, unknown to him she harbours a similar infatuation towards him (not enough to give up her life of crime though). She uses illusions as diversion while she robs th eactual places while using an illusion of herself during her magic show to throw off suspiscion, though she is capable of creating fireballs to attack with, she commonly escapes through her top hat. She originally appeared to steal valuables from Edge City but met her old crush Stanley and makes him an offer to leave with her, he refuses and dons The Mask to stop her. After several failed attempts to woo her, The Mask stops her with his own magic tricks but she ultimately escapes in the end only for the Mask to take her Top Hat escape route.

Other Secondary characters
Baby Forthwright (voiced by Frank Welker): Stanely's neighbor's baby. Wore the mask on three occasions: part one of "The Mask is Always Greener on the Other Side", "Baby's Wild Ride", and "Mutiny of the Bounty Hunter".

Mayor Mortimer Tilton (voiced by Kevin Michael Richardson): the egotistical mayor of Edge City. Though not evident in season one, season two reveals that Mayor Tilton is corrupt (often using the city's budget for elaborate celebrations). In "Goin' for the Green," Mayor Tilton has a nerdy, white assistant (whose name is revealed to be Smedley in the next episode, "Flight as a Feather"). In "Flight as a Feather," it's revealed that Mayor Tilton once dated an exotic dancer named Cookie BaBoom, who crashes his Bavariaville ceremony and threatens to blow herself and the Mayor (to whom she refers as "Mortimer") with two megatons worth of dynamite strapped to her body (which The Mask strips off and makes into a cocktail).

Dr. Arthur Newman (voiced by Ben Stein): Stanely's therapist; doesn't believe that Stanley is The Mask (even after Dr. Newman wore the mask and became a supervillain) and thinks "The Mask" is the side of Stanley who wants to be outrageous and impulsive.

Mrs. Peenman (voiced by Tress MacNeille): Stanley's loud-mouth landlord; often the butt of The Mask's many practical jokes. In "Mask au Gratin," it's revealed that Mrs. Peenman has a niece who works as an archaeologist.