Billy & Mandy

Main Characters

 * Billy (voiced by Richard Steven Horvitz) - William "Billy" is a slow-witted, happy-go-lucky child. He has an extremely low IQ of -5, having been outperformed by a shovel and two candy bracelets on an IQ test. He has an extremely large, pink nose inherited from his father, Harold, wears a blue and white-striped shirt and covers his ginger orange hair (which is inherited from his mother, Gladys) with a red cap. His main affiliations are Grim and Mandy. Mandy is Billy's best friend, though she treats him more like a servant than a friend.
 * Mandy (voiced by Grey DeLisle) - Amanda "Mandy" is a tomboyish heartless girl of vast intelligence and a sinister, manipulative nature. Demanding, rude, and misanthropic, Mandy's antagonistic behavior has left her parents in trembling, quavering perpetual intimidation, and her frightening, cold nature has left her virtually fearless in times of severe supernatural danger or while being faced with menacing, bloodthirsty otherworldly monsters.
 * Grim (voiced by Greg Eagles) - The Grim Reaper is over one hundred and thirty-seven thousand years old (as had been born at the time of the Stone Age) and speaks using a Jamaican accent. The continuity of how Grim got his reaper status and tremendously strong and powerful supernatural powers comes up quite a few times. By losing a limbo contest to Billy and Mandy, Grim is fated to be their "best friend" forever. Unfortunately for the Reaper, the contract legally binds him to them, such that if he were to ever breaks his friendship with them pre-maturely, he would be forced to spend eternity in Underworld Jail as a result of violating his contract.
 * Irwin (voiced by Vanessa Marshall) - Irwin is a pudgy, nerdy boy and a close friend of Billy's. He says the word "yo" regularly. Unlike Mandy and Billy, who show no signs of fear for the frightening, supernatural and magical beings and settings around them when using Grim's magic to venture into the underworld (Mandy because of her fearless, sinister and smart personality and Billy because of his ignorance), Irwin has displayed more signs of cowardice in such situations and seems to be more easily terrified than his friends when he accompanies them on such trips.

Recurring Characters

 * Harold (voiced by Richard Steven Horvitz) - Harold is Billy's father and Gladys's husband. He is an overweight man with a large, bulbous nose and a lofty black pompadour, which houses his brain. Harold resembles his son in appearance and personality, sometimes displaying even more stupidity than Billy himself. Harold's employment is unknown and varies from episode to episode. Despite his low IQ, Harold was accepted in Harvard and was a former Navy Seal. Harold is also known to be afraid of Santa Claus.
 * Gladys (voiced by Jennifer Hale) - Gladys is Billy's mother and Harold's wife. She is a loving, tolerant, and patient, yet mentally unstable woman. This is brought on by having to deal with her family, and Grim as an eternal guest. Gladys has reddish-orange hair and is usually seen wearing a floor-length, lavender dress. She considers Grim a constant threat to her son's safety. In multiple instances, Gladys is seen attacking Grim to protect her son.
 * Pinky and the Brain (voiced by Rob Paulsen and Maurice LaMarche) - Pinky and the Brain are an imbecilic white mouse and his genius companion, respectively, of Endsville's ACME Labs. The Brain is clearly the leader, and attempts to take over the world; Pinky is eccentric and unintelligent, but loyal to the Brain. In 2005, they were spun off into a spin-off series.
 * Grandmama Tanya (voiced by Phil LaMarr) - Grandmama is Irwin's paternal grandmother. She usually ends sentences with "baby", as Irwin does with "yo" and his father with "dude", which seems to be suggesting a family trait. She is also Dracula's wife. Despite her angry demeanor, she seems to care for Irwin, but will sometimes embarrass him. She doesn't like to be challenged or insulted, and has a hatred of hip hop music.
 * Sperg (voiced by Mike Henry) - Sperg is the local bully, who constantly bullies Billy, Irwin, Pud'n, and other kids to no end. He is a husky boy whose preferred method of terrorizing other kids is by administering his lethal wedgies. Despite his physical strength, he is frightened of Mandy because of her toughness and cynical attitude. On his shoulder, he has a heart tattoo that says "Mom" and in "Ecto Cooler" is shown to become furious when Billy reads a poem about Sperg's mother being so ugly that it can cause peoples faces to melt. Ironically, Sperg's mother is shown to actually be a highly attractive woman with dark hair and a more realistic face than other characters.
 * Phil (voiced by Dee Bradley Baker) - Phil is Mandy's father. Like Claire, he is very afraid of Mandy and she seems to have a mental control over him. He and Claire are the only known relatives that Mandy has. He wears a white shirt, dark-yellow glasses and grey pants.
 * Claire (voiced by Bernadette Peters) - Claire is Mandy's mother. She, like her husband, is also terrified of her daughter and does not appear that much in the series. She wears a red-striped sweater and gray pants.
 * Ms. Eleanor Butterbean (voiced by Tress MacNeille) - Ms. Butterbean is Billy and Mandy's uncaring teacher. She often takes naps in class on her desk and detests her job as a teacher. While she is mean to everyone, in a few instances, she is slightly more sensitive, as one time she changes Billy's F to an A, causing the universe to turn inside out, causing her to act like this alter ego of hers.
 * Principal Goodvibes (voiced by Mark Hamill) - Principal Goodvibes is the Paul Lynde-esqe principal of Billy and Mandy's school. His name was legally changed to Goodvibes, and he makes sure that his students feel good to the point of absurdity. It is later revealed in one episode that he sleeps in his car. He also bears a rather uncanny resemblance to politician Ron Paul, in both appearance and speech, who have also influenced the character. He appears to be on good terms with Mandy, being one of the few authority figures for whom she has full respect.
 * Dr. Otto Scratchansniff (voiced by Rob Paulsen) - Doctor Scratchandsniff is Billy and Mandy's school psychiatrist who speaks with a German accent, and who attempts to force Billy and Mandy to be less menacing and troublesome. He often loses patience with them and goes insane, pulling his hair out until he is bald.
 * Hello Nurse (voiced by Jennifer Hale) - Hello Nurse is Billy and Mandy's school's buxom blonde nurse, over whom Billy, Irwin, and Grim fawn. Her appearance usually prompts the boys into affectionate greetings ("Hellooooooo, Nurse!") and leaps into her arms.
 * Slappy Squirrel (voiced by Bernadette Peters) – Slappy Squirrel is a grumpy squirrel cartoon veteran, who lives in a tree on Endsville with her nephew, Skippy Squirrel. She frequently embarks on numerous adventures with Skippy to revive her old days, most of the times against her former cartoon enemies.
 * Skippy Squirrel (voiced by Jane Carr - Skippy is Slappy's nephew, who have the polar opposite personality of his aunt. He dislikes embarking on perils with Slappy as he prefers to watch TV on their house.
 * Hoss Delgado (voiced by Diedrich Bader) - Hoss is a 33-year-old spectral exterminator; a hunter of paranormal creatures. He possesses one real hand and a mechanical one, the latter of which can seemingly produce any tool he desires, most commonly a metal fist or a chainsaw-launching crossbow. For a while he dated Minerva Mink, and their relationship was very dysfunctional. Hoss is known to make incredibly odd and usually completely irrelevant metaphors. He is based Kurt Russell's character Snake Plissken from Escape from New York and his chainsaw hand is inspired by Ash Williams from the Evil Dead series.
 * Fred Fredburger (voiced by C. H. Greenblatt) - Fred Fredburger is a dimwitted, pale green, bipedal furry otherworldly creature resembling an elephant with stubby horns and the tail of a devil. He is depicted as being generally idiotic, infantile, and harmless; he dwells on subjects such as his recent defecation, small facts about himself, and spelling his own name aloud.
 * Goodfeathers (voiced by H. Jon Benjamin (Squit), Dan Castellaneta (Bobby), and Mike Henry (Pesto) ) - The Goodfeathers are an Italian-American trio of pigeons: Squit (gray), Bobby (turquoise), and Pesto (lavender), who work for Endsville's pigeon mafia under orders of the Godpigeon, always getting hurt in the process of doing the mafia's work. The trio is based on Ray Liotta, Robert De Niro, and Joe Pesci's characters in Goodfellas.
 * Nergal (voiced by David Warner) - Nergal is a black-skinned supernatural being with green eyes and wears a business suit, loosely based on the Mesopotamian deity of the same name. He is With the ability to shapeshift he can create several tentacles from his back that can electrocute his victims or turn them into beings looking like himself. What Nergal desires most is having friends, once stating that it is quite lonely in the center of the world. He is generally considered something of a loser and he often becomes histrionic over his failings.
 * Aunt Sis (voiced by Alex Borstein) - Sis is Harold's sister, Gladys' sister-in-law, Billy's paternal aunt, Nergal's wife, and Nergal Jr.'s human mother. She is a sullen-looking woman with glasses, a large nose, and a hairstyle similar to Gladys. She was a spinster who had experienced four-and-a-half-minutes of love in her "pathetic, lonely life" before finally finding her match in the equally-lonely demon Nergal.
 * Nergal Jr. (voiced by Debi Derryberry) - Nergal Jr. is the son of Nergal and Billy's aunt Sis. He is also Billy's first cousin. He looks more like his father than his mother. Like his father, he has the power to shapeshift and most of the time he appears in the form of a kid who rejected his offer of friendship when he first came to the surface. When he takes another shape, he keeps his lime eyes, glasses, green tongue, and sharp, light green teeth.
 * Rita and Runt (voiced by Bernadette Peters and Seth MacFarlane, respectively) - Rita is a disillusioned singing cat who, upon being captured by animal control, meets Runt, a loyal stray dog who thinks Rita is also a dog. Together they go from place to place in search of a new home, which results in their eviction.
 * Doctor Bunsen Honeydew (voiced by Dee Bradley Baker) - Doctor Honeydew is an inventive, yet aloof scientist who frequently performs science experiments and invention demonstrations that typically go awry and has an "affable cluelessness" whenever his assistant, Beaker, is a victim of these presentations. Bunsen serves as a foil for Beaker.
 * Beaker (voiced by Steve Whitmare) - Beaker is Doctor Bunsen's lab assistant who performs ill-fated experiments which often results in him getting seriously injured. Beaker is unable to speak like other humans, and his speech consists of a series of hums and the "meh" sound.
 * Mindy and Buttons (voiced by Debi Derryberry and Frank Welker's vocals) - Buttons is a Rough Collie who takes care of Mindy. Mindy is a young girl who is constantly getting into trouble. Buttons knocks himself out rescuing Mindy, only to be blamed and punished for Mindy's misbehavior by her mother.
 * Minerva Mink (voiced by Julie Brown) - Miverva Mink is an attractive young mink, driving every male, no matter their species, into wild take-filled Tex Avery-styled conniptions at her beauty. She is constantly stalked by Newt, a hunting dachshund dog, who always fails at capturing her for his master duo to being attracted to her. When she spots a sexy male, she goes into multiple lustful spasms of her own like the ones the males give her. She dated Hoss Delgado for some time, much to Newt's sadness.
 * Newt (voiced by Arte Johnson) – Newt is a faithful dachshund of a lazy hunter, who is tasked with hunting and killing Minerva Mink for him. He, however, fails in all of his attempts, as Minerva uses her beauty and attractiveness to reduce him to a bumbling fool.
 * Dracula (voiced by Dave Fennoy) - Dracula is a vampire that was Grim's childhood hero who has normal ears. Dracula talks in the third-person. He is a selfish old man that calls Grim "Skeleton-Man" or "Big Dummy". He gets angry at people for wanting to do things for him. He always wants people to see him dance. When he danced for Tanya she instantly fell in love with him, but he ran away from her when she beat him up, thinking he was a bat. Dracula's appearance and mannerisms are patterned after the blaxploitation movies of the early 70's, most notably Blacula.
 * Chicken Boo (voiced by Frank Welker's vocals) – Chicken Boo is a six-foot-tall chicken. He wishes to live as a human, so he wears flimsy disguises, usually just a hat or a coat, which somehow always fool everyone (except for one person who no one believes.) Unlike other animal characters, Boo can't talk and acts almost exactly like a real chicken, making his disguises all the more absurd.
 * Milkshakes - Milkshakes is Billy's endearing pink pet cat. In spite of his lack of significance in the series, on a couple of occasions he has played a key role; his body has been overtaken supernaturally on two occasions in the past; once by an intellectual tutoring spirit known as a bookworm to help Billy in school and on the other instance by an enraged, vindictive Mandy, whose body had been possessed by a clowning Billy earlier in the episode.

Secondary and One-Time Characters

 * Nigel Planter (voiced by Jake Thomas - Nigel Planter is a spoof of Harry Potter, a boy with glasses and an "L"-shaped scar on his forehead (it was later revealed to be nothing more than a pen mark). He's a young whiny wizard from Weaselthorpe House at Toadblatt's School of Sorcery. He is often overconfident and holds a deluded self-image, often taking credit for things he did not do.
 * Judge Roy Spleen (voiced by Hank Azaria - Judge Spleen is the judge of the Underworld Court. He hates Fred Fredburger, who pester him constantly.