The following is a list of characters in Fanboy and Chum Chum.
Fanboy is an enthusiastic fan of comic books, fantasy, science fiction, and action figures. Fanboy, the show's protagonist, wears a purple mask, cape, and gloves, green tights, black high-top sneakers, and his trusty underwear on the outside of his costume and has a glass eye revealed, Fanboy originally wears a grey unitard. Fanboy has an active imagination, a zeal for fun, frolic, and adventure, and he enjoys spending all of his time with his best pal, Chum Chum. His unique and simple life perspective tends to cause him trouble, but he usually finds a way to weasel out of any consequences. Voiced by David Hornsby.
Chum Chum is the show's deuteragonist as Fanboy's best friend and sidekick. Although he is younger than the other main characters, he is still in the same class as them. Show creator Eric Robles explained on the Nickelodeon message board that this is because Fanboy snuck him into his class and the teacher never noticed the age difference. Like Fanboy, Chum Chum doesn't appear to have any super powers (except in the episode "Fanboyfriend," when he absorbed the radiation waves and picked up a number of super powers by the end of the episode). Chum Chum is extremely energetic and high-spirited, and possesses an indomitable enthusiasm and childlike jocularity. Chum Chum wears a black mask and gloves, orange tights, black high-top sneakers, and his underwear on the outside of his costume. Chum Chum seems to be incapable of achieving more than 3 points on Boog's "Chimp Chomp" video game, although Chum Chum is ecstatic even when he loses. Voiced by Nika Futterman. In the pilot from Random! Cartoons, he was voiced by Nancy Cartwright.
Kyle is an occasional tritagonist who sometimes acts as an antagonist. He is a wizard and is the only character with actual powers, other than his rival Sigmund the Sorcerer. Kyle has a pessimistic attitude towards anything involving Fanboy and Chum Chum. He got expelled from his wizard school, Milkweed Academy, after turning his teacher into a raspberry flan ("Delicious old fool," Kyle said of him). Kyle is now reluctantly enrolled in Fanboy and Chum Chum's regular public school, and seems to have very few friends. In Kyle's debut episode, "Wizboy", Fanboy and Chum Chum did not recognize that Kyle possesses wizardly powers. After that, the boys seem quite aware, such as in "Excuse Me." Kyle truly detests Fanboy and Chum Chum's lack of intelligence, but he occasionally craves their friendship, and is capable of working with them at times. He wears a scarlet and yellow striped shirt with jeans, black high tops, and a black cape. He has red hair and very large front teeth with braces and he speaks in a British accent. He often suffers painful indignities, often a result of Fanboy and Chum Chum's shenanigans, but Kyle never seems to be any worse for the wear. He calls himself "Kyle the conjurer." Voiced by Jamie Kennedy.
Boogregard "Boog" Shlizetti is a short-tempered bop-happy bully who is obsessed with the video game Chimp Chomp, which he plays at the Frosty Mart, often instead of working. He has mentioned twice that he grew up in a plastic bubble (an homage to John Travolta, who starred in The Boy in the Plastic Bubble), and it becomes a major plot point in "Fanboy in the Plastic Bubble." Boog even talks like Travolta's character, Vinnie Barbarino, in Welcome Back, Kotter. He has a prized car named Sandy, which is a possible reference to the movie Grease. He is an antagonist of the show. Voiced by Jeff Glen Bennett.
Lenny is the accident prone junior manager of the Frosty Mart. He finds Fanboy and Chum Chum irritating and sometimes gets a "stress twitch" when annoyed by them. His first appearance was in "Dollar Day." Voiced by Wyatt Cenac. In the pilot from Random! Cartoons, he was voiced by Jeff Bennett and had orange hair instead of black and was white instead of black.
Ozwald "Oz" Harmounian is occasionally a tritagonist of the show. Fanboy and Chum Chum think he is "the most knowledgeable human being ever," yet in reality, he is a nerdish know-it-all who lives with his elderly mother. He often says "seriously" as a means of punctuating his opinions. He runs a comic shop called Oz Comix, and he has a vast stock of comics and collectibles, all of which he hoards, and none of which he is willing to sell. He is plump, has a ponytail, a soul patch beard and wears a black high collared leather jacket. It is not known how old Oz is, but he is quite likely of the age when it is no longer cool to be living with one's mother. Voiced by Josh Duhamel.
Yo is Fanboy and Chum Chum's friend and an occasional tritagonist. Yo is a sweet, happy-go-lucky girl, and loves her digital pet cat, Scampers, which is made by Yamaguchi (a parody of Tamagotchi). She is sometimes an antagonist. She has a rather insane crush on Chum Chum and appears in "Saving Private Chum Chum" to help him out when Mr. Mufflin keeps him at night. She is shown to be a talented prankster, dominating Fanboy on Prank Day. Voiced by Dyana Liu.
Mr. Hank Mufflin is Fanboy and Chum Chum's grouchy yet often playful teacher. Mufflin usually considers the boys to be annoying and beneath recognition. His dispassion for teaching is punctuated by his dull vocal tone. Occasionally, however, Mufflin will indulge himself a shred of youthful exuberance. He is potentially senile and he hates almost every aspect of his job. According to show canon, Mufflin will be able to retire in approximately 12 years. He has a gravely, monotonous voice and a lazy eye. Voiced by Jeff Glen Bennett.
Janitor Russ Poopatine is a janitor at Fanboy and Chum Chum's school and another major antagonist. He is a parody of Emperor Palpatine from Star Wars. He is a pale, skinny, gnarled old man who wears a dark hooded shirt. Several of his lines in his debut episode "The Janitor Strikes Back" (the title, of course a parody of The Empire Strikes Back) are direct parodies of lines spoken by Palpatine and Darth Vader. For example, in The Janitor Strikes Back, Poopatine says, "And now gum, you will die," which is a parody of "and now Young Skywalker, you will die.". In episode "Fanboy Stinks", Poopatine attempts to wrangle Chum Chum's pecan log stuck to the floor, falls over and says "The force is strong with this pecan log". Poopatine rides around in a cart named Brenda, who communicates by beeping in a manner similar to R2D2. Poopatine has a strong hatred of gum and saltwater taffy. Poopatine tries to destroy the bubble gum monster Yum Yum, until it saves his life. In "The Janitor's Apprentice", it is revealed he has a trash collection and a trash receptacle called the "Dump Star", a parody of the Death Star. A running gag is that whenever Poopatine's name is spoken aloud, Chum Chum (or Cheech in "The Janitor Strikes Back") says, "Poop!". Voiced by Steve Tompkins.
- Man-Arctica is an ice-themed superhero who loves milk and cookies, (but not cookies and milk after getting sick the first time he tried them). His biggest fans are Fanboy, Chum Chum, and Fedora Man. Man-Arctica has appeared in a number of episodes. Voiced by Jeff Bennett.
- Fankylechum was originally a mixed up name made up by Fanboy, Chum Chum, and Kyle to fool Mr. Mufflin into getting them out of school, but their plan fails when he calls an actual character who has the name and excuses him from all school forever but is later actually back in the school. He wears glasses and a school uniform. He appears in "Excuse Me" and reappears in "Saving Private Chum Chum" as one of Fanboy's helpers along with Yo, Chris Chuggy, Duke, Lupe, Michael Johnson and Kyle. Voiced by Jamie Kennedy.
- Chris Chuggy is a classmate of Fanboy and Chum Chum's. He seems unable to form sentences or words, but only utters a low-pitched "wah" sound as response. He also appears in "Saving Private Chum Chum" as one of Fanboy's helpers. He is roundish with orange hair.
- Scrivener Elf is an elf Kyle creates in "The Janitor Strikes Back" to do his homework and other tasks. He is seen in other episodes writing notes for Kyle. He is purple and wears burlap clothes like people in the Middle Ages. He also has buck teeth and pointed ears. He is rather shiftless and is the closest thing to being one of Kyle's friends. Voiced by Jeff Bennett.
- Lupe is one of Fanboy and Chum Chum's schoolmates. She once mentioned that she has an uncle who married a chicken and was as crazy as Chum Chum. In the episode "Fanboyfriend," she forms a crush on Fanboy after he squished a spider that was near her. She has also punched Kyle in "Wizboy," after he descended himself from levitation in her lunch, but on "The Janitor Strikes Back", Kyle was showing her magic. She also appeared in "Saving Private Chum Chum" where she was one of the students to help Chum Chum. She has a Spanish accent and is voiced by Candi Milo.
- Dollar-nator is a sophisticated computerized intelligence system built by Fanboy in the future, and sent back in time by Fanboy to bail Fanboy and Chum Chum out of a jam in 'Dollar Day'. He has made numerous appearances on the show and he is someone the boys can rely on in a jam. Dollar-nator has many surprise skills and talents. He is an obvious parody of The Terminator, as he has a gap between his teeth, a thick Austrian accent and materialized from the future. Dollar-nator is made up of parts from a Chimp Chomp machine, a ping-pong video game, a restaurant grade hot dog steamer, a microwave oven and other components as yet defined. Voiced by Jeff Bennett.
- Kyle's Necronomicon is a talking book of spells who helps out Kyle on occasion. It appears in "Chicken Pox", "Little Glop of Horrors", "Sigmund the Sorcerer" and soon to come, "The Book Report of the Dead". Voiced by Jeff Bennett.
- Sigmund the Sorcerer and Harold the Unbelivable is Kyle and Wally's more successful and skilled wizard rival from Kyle's old school, Milkweed Academy. Sigmund appeared in the Season 1 episode, "Sigmund the Sorcerer". He is Fanboy and Chum Chum's idol for having his own magic show. Sigmund has white hair and wears elegant clothes under a long jacket, and wears fingerless gloves. . He may have more fame and fortune, but Kyle may have the one thing Sigmund and Harold might not have, Fanboy and Chum Chum as friends. Voiced by Jeff Bennett.
- Lunch Lady Cram is the new strict lunch lady who replaces the former lunch lady. Cram's most popular dish, glop, is made from an unappealing mound of meat, sauce and other horror. She doesn't let anyone out of the cafeteria until they clean their tray and she doesn't allow anyone to throw away her food. She also appeared in "Refill Madness", "Excuse Me", "Pick A Nose" and "Norse Code". She is revealed to have gotten her powers from her hairnet and later falls in love with Thorvald and goes with him to Valhalla. Voiced by Candi Milo.
- Thorvald the Red is a Viking who debuted in "Norse-ing Around". He thawed from inside of a giant ice pop Fanboy and Chum Chum had made in their freezer. In Norse-ing Around, Thorvald is consumed with the need to get to Valhalla, one of the Norse versions of heaven. Thorvald later appears in "Norse Code" where he loses his battle axe in the school and is forced to work for Lunch Lady Cram. Thorvald gets his battle axe back from her and carries them both off to Valhalla. He is named after the Norse god Thor and is voiced by Nolan North.
- Berry the Ice Monster is a small pink creature who lives inside the Frosty Freezy Freeze machine at the Frosty Mart. He creates Frosty Freezy Freeze with his ice breath. In "Berry Sick", he becomes ill and is unable to produce any more Frosty Freezy Freeze. Fanboy and Chum Chum kidnap him and pretend to be doctors attempting to cure him, when in actuality, they want to keep him so that they can have Frosty Freezy Freeze. He also appeared in the 8-minute pilot, though in this appearance he was rather large, monstrous and had no feet. He was created from the combination of Frosty Freezy Freeze and Ice-Monster Bun Bun. He is voiced by Kevin Michael Richardson.
- Fedora Man He appears in "The Hard Sell" where he bought a pickle jar. He wears a spring green tuxedo and a fedora. He reappears as the title character of the episode "Secret Shopper" where he also has a wide collection of Man-arctica merchandise. Voiced by Jeff Bennett.
- Global Warmer is an upcoming super-villain and archenemy of Man-Arctica who will appear in "Stan-Arctica" and "Man-arctica the Ride". Voiced by Jeff Bennett
- Oz's Mom is a single mother committed to teaching her son that the only way to run a successful business is by selling. She is usually met with great resistance from Oz, even though she is in control of the comic shop's purse strings. Voiced by Estelle Harris.
- Chimp Chomp is a Donkey Kong parody video game featuring a chimp who is trying to take an ape's bananas. The ape sits at the top of a palm tree and throws energy balls at the chimp. Chimp Chomp has spawned two movies within the series. The Chimp Chomp machine in the Frosty Mart tends to get destroyed by Fanboy and Chum Chum in each episode it appears.
- Precious is the pet pig of Mr. Mufflin's class, and was obtained via a door-to-door pig salesman. Fanboy attempted to teach him martial arts in the episode "Precious Pig." Even though he was only a one-time character, he also made a cameo in two brief scenes in "Night Morning," on the roof, howling like a wolf and playing a recorder flute. He also was in "Norse-ing Around" when Chum Chum was riding him like a horse for gold stars. In "Strings Attached," it is revealed that Precious is a burglar that robs banks. Voiced by Dee Bradley Baker.
- Michael Johnson is a classmate of Fanboy and Chum Chum. He is an obvious parody of and tribute to Michael Jackson, as Johnson wears leather pants and jacket similar to those worn by Michael Jackson in his "Thriller" video. Like Jackson, Johnson often makes high-pitched exclamations such as "Hee hee," "Shamoan," etc. He is often shown doing the moonwalk as opposed to walking. Voiced by Wyatt Cenac.
- Duke is a classmate of Fanboy and Chum Chum's. He is tall, wears a 5 on his shirt and has blonde hair. He ends every sentence with "man." Voiced by Jeff Bennett.
- Dr. Acula is a vampire plastic surgeon who gave Chum Chum a neck when Fanboy believed he was vampire. Chum Chum wanted to be his immortal companion upon learning vampires are not mortal. Chum Chum wanted to have a neck so Fanboy would bite him and he could be immortal as well. At the end of the episode, Dr. Acula bites Fanboy a second time (having unknowingly bitten him some time in the beginning of the episode) and Fanboy becomes a vampire. He then bites Chum Chum and he becomes a vampire as well. Dr. Acula, gaining Fanboy's irritating personality, felt the urge to play video games and drink Frosty Freezy Freezes and was unable to control his flatulence. He is based on the Dracula archetype and is destroyed by the morning sun while trying to get back to his coffin. Afterwards, Fanboy turns into "Fangboy" for real and bites Chum Chum's new neck turning him into a vampire as well. Then they walk into the Frosty Mart and bite Boog, likely turning him into a vampire. He is only seen in "Fangboy" due to his death and was voiced by Jeff Bennett.
- Fanbot is a robotic version of Fanboy that appears in "I, Fanbot". In a hare-brained scheme to pass a standardized test, Fanboy installs his brain into Fanbot, instead of installing Fanbot's brain chip in Fanboy's own body. As a result, everyone fails the test.
- Mist Monster is a hallucination that Boog has when he plays a video game for 2 1/2 days straight. He believes it is a monster but when he puts on glasses he realizes he was just hallucinating. At the end of the episode he is eaten by the real monster. He slightly resembles Chum Chum sitting atop Fanboy's head, as that was Boog's hallucination of them. Voiced by Jeff Bennett.
- Monster under bed is a monster under Fanboy's bed that appears in 'Night Morning'. It is only seen for a brief second and only its tentacles are seen. Voiced by Dee Bradley Baker
- Grandboy is Fanboy's grandfather. Although he is not seen, he is mentioned by Fanboy in "I, Fanbot".
- Scampers is one of Yo's Yamaguchi digital cats. Fanboy and Chum Chum were supposed to take care of Scampers over the weekend while Yo entertained a house guest. Scampers's constant need for cupcakes angered Fanboy, who then overfed him and caused Scampers to "power down". Fanboy and Chum Chum buried Scampers in a digital pet graveyard. Scampers returned as a zombie. Scampers is destroyed and buried multiple times, regenerating each time until Oz crushes Scampers with a battle hammer. Scampers mysteriously returns, only now much larger. Oz is unable to defeat Scampers, but his mother conveniently walked in with a batch of cupcakes. This calmed Scampers down, though he still ate Chum Chum. Voiced by Dee Bradley Baker.
- Yum Yum is a cycloptic bubble gum creature created by Fanboy and Chum Chum. He is one of their best friends, and appears in the opening sequence. He sat on Kyle, and was also seen in Boog's car in "Refill Madness". He is absentminded, speaks in third person and is voiced by John DiMaggio.
- Fanman is a superhero who appeared in the Random! Cartoons 8-minute short "Fanboy". His costume is the basis for Fanboy's costume, however, in the actual series, references to Fanman appear to have been replaced with Man-Arctica. He was voiced by Scott Grimes.
- Sprinkles is the class bear of Fanboy and Chum Chum. He was a cub before the series but is now an adult brown bear. He also appeared in "Excuse Me" when Mr. Mufflin is tricked by Kyle, Fanboy, and Chum Chum into wrestling it by one of Scrivener Elf's notes he also appeared in "Prank Masters" when he was attacking Fanboy as a prank from Chum Chum and later Yo. Voiced by Dee Bradley Baker.
- Stinks A life-form that spawns from Fanboy's right hand after he goes several days without bathing. Stinks has the attitude of a New York mobster and has mushrooms for eyes.
- Muk Muk A female cousin of Chum Chum. Her appearance resembles Chum Chum's, though she sports pigtails and a dress. She hails from the wealthy city of West Apetown. Muk Muk tends to leap around constantly, which makes corralling her quite difficult for Chum Chum. She loves to eat and she favors guttural sounds over speech. Contrary to what some fans have assumed, her name is not "Chum Chum" spelled backwards. Voiced by Nika Futterman.
- Crabulus: Destroyer of Worlds is an action figure who is a crab in "The Hard Sell". He has an exercise video "Crabulus: Destroyer of Flab". Voiced by Jeff Bennett.
- Moppy is a mop that Fanboy assembled as a date for his school dance in "Moppy Dearest". While she appears to only be a dolled-up mop in a rolling bucket, some of the other characters acknowledge her personality. Yo, Lupe and Francine, for example, treat her with kindness. Janitor Poopatine seems to admire her, much to Brenda's disappointment.
- Cheech is a buck-toothed boy in Mr. Mufflin's class. He was the first person to say "Poop!" to Janitor Poopatine. Voiced by Nika Futterman.
- Nancy Pancy Is a girl nerd in Mr Mufflin's class. Voiced by Kari Wahlgren in "Fanboy Stinks" and Nika Futterman in "Fanboy A'hoy".
- Francine is a diva in Mr. Mufflin's class. She talks like a Valley Girl and doesn't really care about much. Voiced by Candi Milo.
- Cher Leader is the peppy cheerleader in Mr. Mufflin's class. She is a triplet, and has the nickname Of "Cheer" because of her winning personality. She and her sisters by Kari Wahlgren in "Fanboy Stinks" and Candi Milo in all other appearances.
- Agent 08 is an octopus cartoon character who is a secret agent. Oz collected the toy of Agent 08 and bought it. Its ink is very acidic. It shocked Fanboy and Chum Chum many times and once almost blew them up.
- Agent Johnson is a secret agent who attempted to recall Agent 8 in "Total Recall". He also appears st the end of "Jingle Fever" to congratulate Fanboy and Chum Chum for their jingle composition and awarded them their 1 million Frosty Bucks. Voiced by Jeff Bennett.
- Cuppy Is a living Frosty Freezy Freeze cup which Fanboy and Chum Chum keep as a pet. Boog and Lenny make many attempts to get it away from the boys after discovering that it can be used for a free refill.
- Ms. Olive is a preschool teacher who appears in "Marsha Marsha Marsha". She also appears as a French teacher named Madame LaVache in "Excuse Me" with a French accent. She also reappeared in "Strings Attached" where she has a baby.
- Marsha was a sweet, successful student until Fanboy ruined her life by sneezing on her placement test, rendering it illegible. As a result, she received a failing grade, and was sentenced to repeat kindergarten. When Fanboy and Chum Chum encounter her in "Marsha, Marsha, Marsha", she has gone nutty and she attempts to kill Fanboy. Voiced by Candi Milo
- Professor Flan is a teacher of Kyle's from Milkweed that he turned into raspberry flan. Voiced by Jim Cummings