| Character | Notable powers | Notes | Voice Actor |
| The Angry Red Herring | Also referred to as simply the Red Herring, he can rub petroleum jelly on himself to escape the grasps of superheroes. He also has machine guns in place of eyes in his fish costume. | Real identity is Milton Roe, who is a fishmonger and jewel thief | Kevin Schon |
| Baron Violent | Has a belt he uses to adjust his muscular mass, and in turn, his strength, often to overblown proportion | Without the belt enhancement, he is not over five feet tall. | Brian Peck |
| Barry Hubris | Has a shield with a conductor in it that allows Barry to crush things he wouldn't be able to normally. | He uses the name "the Tick", unaware that a hero exists with the same name. He claims to be a hero himself, but is only in it for the fame. | Jim Cummings |
| Betty: Queen of the Ants | Speech and Sentience | Basically a normal ant that can talk | Cathy Moriarty |
| Brainchild | Super intelligence, Inventor | Gave himself a glass skull to show off his large brain. He acts as a villain on principle alone, and has no real motivation other than causing chaos in ways such as attempting to gravitate the Moon into colliding with Earth. In some way, he is a spoof of Leader. | Rob Paulsen, Stuart Stone |
| The Breadmaster | Creates baked goods that are used as weapons | Expelled from baking college for "pursuing perverse baking experiments". | Roddy McDowell, Jess Harnell |
| Chairface Chippendale | | A crime lord and evil mastermind who has a chair for a head. He is also an expert at fencing. | Tony Jay |
| The Deadly Bulb | Has a light socket on the top of his head in which a giant light bulb usually sits. As transport, he uses a hot air balloon in the shape of a skull. | Inexplicably has a living pig on the end of his right leg—which serves as the basis for his later name, Pigleg | Maurice LaMarche |
| The Deadly Nose | Has the double-barrel muzzle of a gun for a nose | | N/A |
| Dinosaur Neil | Can turn into a giant dinosaur | Although not technically evil, Dinosaur Neil was originally a paleontologist who accidentally ate dinosaur DNA and must take a special medicine to keep himself from transforming and going on thoughtless rampages. He later marries Arthur's sister, Dot. | Danny Mann |
| Dr. Julius Pendecker | Crazy inventor | A mumbling mad scientist and rival of Mr. Mental | Mark Hamill |
| Dyna-mole | | A man resembling a mole who is continually ensconced in sticks of dynamite. His voice is an impersonation of Peter Lorre | Pat Fraley |
| Eastern-Bloc Robot Cowboy | | A cyberneticist who transferred his brain to a walking, talking vending machine. Has an unfortunate weakness to quarters. | Pat Fraley |
| El Seed | Knows how to make chemicals that manipulate plants | An anthropomorphic sunflower wearing a green matador uniform. His name is a play on the historic Spanish hero El Cid. | Ed Gilbert |
| The Evil Midnight Bomber What Bombs at Midnight | Explosives expert | A crazed bomber who tries to blow up establishments of all sorts, preferably places where superheroes are known to gather, such as the Comet Club. Rarely goes a second without mumbling to himself recollections of snippets of conversation with an unknown second party, some glorifying himself, others suggesting a bad end between the two. | Maurice LaMarche |
| Eyebrows Mulligan | | A gangster with long eyebrows | Townsend Coleman |
| The Fin | He has super-intelligence | A talking dolphin who formerly performed in Reno, Nevada, who turns to evil after being annoyed constantly by his trainers Soren and Frederica | Maurice LaMarche |
| The Guy With Ears Like Little Raisins | | A gangster who has ears like little raisins | N/A |
| Harriet Curse | A villain with dark powers. | She resembles Oedipus' mother from the comics. | N/A |
| Headless Henderson | | A villain with no head | N/A |
| The Heys | | A nihilistic alien race that can only say "Hey" who worship nothing and want to destroy the universe. For a peculiar reason, they all wear suits exactly like Arthur's moth suit. | Hank Saroyan and Steve Susskind |
| The Hotel Manager | | A man from the distant future who opens up a restaurant in the distant past. | Maurice LaMarche |
| The Human Ton and Handy | The Human Ton has super-strength. Handy can speak while the Human Ton's mouth is otherwise preoccupied, such as when biting the head of the Tick | An enormous dim-witted man, who is the parody of the Blob from the X-Men comics and his verbose, much more intelligent hand puppet who longs to be "a real boy". Handy apparently has an affinity for encouraging people to read literature rather than watch television; his catchphrase, fittingly, is therefore "Read a book!" Handy is a parody of Batman villain Scarface. | Maurice LaMarche |
| The Idea Men | | A group of men wearing suits, white gloves, and large metal masks that muffle their voices to the point that their ransom demands cannot be heard. They travel via zeppelin. | Ed Gilbert |
| The Indigestible Man | Incapable of being digested | A freelance villain hired by Chairface Chippendale, sporting wild white hair. He uses his abilities to navigate large bodies, such as that of the transformed Dinosaur Neil. | Ed Gilbert |
| Jack Tuber: Man of a Thousand Faces | Has a potato for a head | A parody of Mr. Potato Head. | Kevin Schon |
| Jim Rage | | A special agent with Project S.H.A.V.E. that has been pursuing an elusive mustache—so much so that his S.H.A.V.E. allies ultimately end up ending their affiliation with him. He wears an eyepatch—not because he is missing an eye, but rather because he thinks it makes him look cool. Likely a parody of Nick Fury | Brad Garrett |
| Joseph Stalin | | In actual history, Joseph Stalin was the dictator of Russia. In this show, Joseph Stalin was one of the Terror's cronies whose Atomic Robot Zombie Cronies that he used in his plans to conquer Earth were thwarted by the Decency Squad. Many years later, the Terror mistook Stalingrad as the actual Stalin until Stalingrad corrected him. | N/A |
| Lava-Man | Beings made entirely of lava, and the enemy of the Mole people. | One in particular was sent to terminate the Mole King. | Townsend Coleman |
| Lou Salazar: The Sewer Czar | | A corrupt civil agent turned evil and enemy of Sewer Urchin. | John Mariano |
| The Man-Eating Cow | A cow capable of eating humans | Despite her name, she has never actually been seen eating anyone. | Townsend Coleman |
| Mr. Mental | Mind control and telepathy | Despite his plans to use his mind control to take over Earth, Mr. Mental is often thwarted due to either bad luck or having the lack of competent help. | Canned Walla, Jim Cummings |
| The Mother of Invention | Super intelligence | An androgynous man dressed as a stereotypical mother who creates a time helmet to steal the credit for every invention ever made by kidnapping Leonardo da Vinci, Benjamin Franklin, Thomas Edison, Johannes Gutenberg, George Washington Carver, and a cavewoman named Wheel, who allegedly invented the wheel. He would then completely eradicate the past and re-invent the inventions in the future | Paul Williams |
| Multiple Santa | Being shocked by high-voltage currents creates electric clones of him | He was a criminal who was "granted" his power after stealing a charity worker's Santa Claus suit in an attempt to escape from the police and being accidentally chased off the roof of a building and into a large electric billboard by the Tick. | Jim Cummings |
| Octo-Paginini | | From Belgium; has three sets of arms, for a total of eight limbs; can play several violins simultaneously | Xander Berkeley |
| Octo Raymond | | An octopus-themed enemy. He served as the conductor for the Mollusk Band and provided music at the Enemy Awards | N/A |
| Omnipotus: The Devourer of Worlds | | A parody of the Marvel character Galactus. He is an enormous being that feeds on celestial bodies. Although Tick doesn't really consider Omnipotus himself evil, he does consider eating planets an evil act, according to the book "Mighty Blue Justice!". He has oddly small feet for his size. After Tick convinced him not to eat Earth, he did end up taking a large bite out of the Moon, which remained in that state for the rest of the series' run. | Ron Feinberg |
| The Ottoman Empress | Ability to control furniture | Also known as simply the Ottoman; she is a beautiful red-head woman who falls in love with Die Fledermaus in an attempt to convert him to evil | Mary Kay Bergman |
| Pineapple Pokopo | Above-average strength | The leader of a small nation known as Pokoponesia that is known for two things: sharks and pineapples. His head resembles a pineapple | Dorian Harewood |
| Proto-Clown | Superhuman strength | The product of genetic engineering by a clowning engineer named Bud Frontier in his attempt to make a super-clown with the capacity to amuse and entertain more people than a normal clown. He hates being laughed at, however, and if he is laughed at, it usually results in him going on a destructive, violent rampage. Loosely based on the Incredible Hulk. | Kevin Schon |
| Sheila Eel | A female villain that wears an electric eel as a garment | She once shocked the Guy With Ears Like Little Raisins when he got too close. Her name is a reference to the singer Sheila E. | N/A |
| Stalingrad | Encyclopedic knowledge of Stalin | A graduate student who looks like and bases his villainy on the work of Joseph Stalin. The Terror constantly gets the two confused as he knew the real Stalin. Stalingrad later falls in love with Tuun-La: Not of This Earth and they later leave Earth together. | Jim Cummings |
| The Sub-Human | | A Golden Age villain that fought the Decency Squad. He wears a miniature submarine on his head. | Jess Harnell |
| The Swiss Industrial Spies | | A group of Swiss spies that targeted the notebook of Dr. J.J. Eureka Vatos, inventor of the moth suit Arthur wears, and even tried to steal the pants from Arthur's suit in an attempt to replicate it. | Various voices |
| The Terror | Inventor, super-strong in his youth | "The greatest villain of the 20th century... and maybe some of the 19th". He once punched out President Teddy Roosevelt. According to Arthur, he is approximately 117 years old. | Rob Paulsen |
| Terry | | The son of the Terror and a retired insurance adjuster who tries a brief stint walking in his father's footsteps. | Peter Bergman |
| Thrakkorzog | | An alien creature from Dimension 14B. He had an apartment across the hall from Arthur and the Tick. His voice is an impersonation of James Mason | Jim Cummings |
| Tuun-La, Not of this Earth | Can apparently tuck in her legs and shoot flame from where they were. | An alien that is a brief ally of the Terror alongside Stalingrad, Human Ton and Handy, and Man-Eating Cow. Tuun-La: Not of This Earth later falls in love with Stalingrad and they later leave Earth together. | Pat Musick |
| Uncle Creamy | Being made of ice cream, he can shoot ice cream from his hands, forming it into the shapes he wants, and is very difficult to hurt physically | A result of an industrial accident. Spoof of Clayface and Sandman. May not be a villain at heart as he once quoted "I'm not a villain, I'm vanilla". | Bobcat Goldthwait |
| Uncle Creamy II | He can fly with his rocket boots and has a missile launcher on his left arm | A former KGB agent. Spoof of the many Clayfaces | Kevin Schon |
| Venus | Hypnotizes men to become her love slaves and do whatever she wants | Bears some resemblance to the Venus of Willendorf. Venus' wimpy husband Milo is her sidekick | Linda Gary |
| Wally Head | | The leader of the Deertown Aztecs, a baseball team gone bad. He and his baseball team have a lifestyle similar to the Aztecs, constantly adding the phrase "Itlan" to whatever they say. | Phil Austin |
| Whirling Scottish Devil | He can spin at high speeds | While the Tick was stranded in space and believed to be dead, Arthur attempted to apprehend this criminal solo. Upon the Tick's return from space aboard Omnipotus' rocket-powered shoe, he knocks the head off of a Tick statue sculpted in his honor by The City, which falls onto the Devil and knocks him out. | Pat Fraley |
| The Yes Men | N/A | N/A | N/A |
| Character | Notable powers | Notes | Voice Actor |
| Arthur Clone | | A clone of Arthur created by Thrakkorzog. It is only capable of saying the phrase "I Arthur". | Micky Dolenz |
| Bee Twins | | Bee-themed female villains that are El Seed's henchmen. | Pat Musick |
| Boils Brown | | One of Chairface Chippendale's henchmen, whose face is covered in boils. | N/A |
| Buttery Pat | Can slip through tight spaces due to being made of butter. | The Breadmaster's sidekick | Jess Harnell |
| The Crease | | Has a large facial crease that covers his eyes | Kevin Schon, Pat Fraley |
| Dean | Super-strength | Chairface Chippendale's henchman who has a butterfly nut for a head. Referred to as the Butterfly-Nutcase in comics and other media. | N/A |
| Filth | | Lou Salazar's henchmen | David Lander and Chuck McCann |
| The Forehead | | One of Chairface Chippendale's henchmen who has a large forehead. | Rob Paulsen |
| Fortissimo Brothers | They have the strength of 10 men where Tick was uncertain whether that means 5 men apiece or twenty altogether | Octo Paganini's henchmen. | Philip Proctor |
| Gingerbread Men | | A bunch of Gingerbread Men created by Breadmaster. They can be rendered immobile upon becoming stale. | N/A |
| Hooks Horowitz | | A henchman of Chairface Chippendale who has hooks for hands. His face is never seen, and in the comics, he does not even have a head at all. | N/A |
| Mad Nanny | Wears robotic armor | Real name Miriam Brunch, the Mad Nanny is Brainchild's babysitter whom he brainwashed and outfitted in robotic armor. | Pat Musick |
| Milo | | Venus' husband and sidekick, whose inventing mind created a ray that made the Tick and Arthur's arms fall off and placed them on the crudely made Evil Tick and Arthur robots which were used to frame them. Wears a poorly made angel costume. | Gerrit Graham |
| Minda | | Mr. Mental's assistant and sidekick. However, she later became a receptionist at Captain Sanity's Superhero Sanitarium after she grew tired of his plans for world conquest. | Jennifer Darling |
| Professor Chromedome | Inventor | Chairface Chippendale's mad scientist henchman who wears a tight metal helmet covering his scalp. | Hamilton Camp |
| Rosebud | Super-strength | Rosebud is a large rose monster created by El Seed to help steal the 400 Year Bloom. | Townsend Coleman |
| Skippy | | Originally Brainchild's dog, his brain was placed in a robotic dog body after he was hit by a car while chasing one coming toward him. | Roger Rose |
| Socket and Watt | | Deadly Bulb's henchmen | Paul Eiding and Jess Harnell |
| Tick-Bot and Arthur-Bot | | Crudely made robot look-a-likes of the Tick and Arthur that were created by Milo and had the stolen arms of Tick and Arthur, whom they were used to frame for various crimes | N/A |
| Tick Clone | | A clone of Tick created by Thrakkorzog. | N/A |
| Zipperneck | | One of Chairface Chippendale's henchmen. The zipper on his neck can be unzipped to reveal the interior of his esophagus, which is so grotesque that heroes will cease fighting just to avoid looking at it. He was also once mentioned on the 2001 live action show. | Pat Fraley |