This is a list of characters in the American film Jimmy Neutron: Boy Genius, its subsequent television series The Adventures of Jimmy Neutron, Boy Genius and other media of the franchise.

Cast table Character Voiced by Jimmy Neutron: The Adventures of Jimmy Neutron, Boy Genius The Jimmy Timmy Power Hour Planet Sheen Count 1 2 3 1 2 3 1a 1b Jimmy Neutron Debi Derryberry colspan="7" colspan="2" 59 Sheen Estevez Jeffrey Garcia colspan="9" 87 Carl Wheezer Rob Paulsen colspan="7" 65 Cindy Vortex Carolyn Lawrence colspan="7" colspan="2" 59 Libby Folfax Crystal Scales colspan="7" colspan="2" 45 Goddard Frank Welker colspan="7" colspan="2" 57 Hugh Neutron Mark DeCarlo colspan="7" colspan="2" 57 Judy Neutron Megan Cavanagh colspan="7" colspan="2" 49 Ms. Winfred Fowl Andrea Martin colspan="3" colspan="5" 49 King Goobot V Patrick StewartS. Scott Bullock colspan="5" 3 Finbarr Calamitous Tim Curry colspan="3" colspan="3" 8 Emperor Fred Tatasciore colspan="7" colspan="2" 44 Doppy Doppweiller Rob Paulsen colspan="7" colspan="2" 44 Nesmith Bob Joles colspan="7" colspan="2" 38 Pinter Thomas Lennon colspan="7" colspan="2" 30 Princess Oom Candi Milo colspan="7" colspan="2" 30 Aseefa Soleil Moon Frye colspan="7" colspan="2" 26 Dorkus Jeff Bennett colspan="7" colspan="2" 22

Main Jimmy Neutron

James Isaac "Jimmy" Neutron (voiced by Debi Derryberry) is an extremely intelligent 11-year-old boy who uses lots of scientific knowledge and inventions to solve problems, most of which he causes himself. His name is a reference to Isaac Newton. He is the son of Judy and Hugh Neutron. Although he is a genius, he is a kid at heart and has more often than not proven so. Due to the events in Retroville, Jimmy is key in resolving most situations. Jimmy will usually exclaim "Gotta think..." when he begins formulating a solution for the dilemma, accessing a vast wealth of information gathered during the dilemma. Once he has developed a plan, he usually exclaims "Brain blast!" His best friends are Sheen Estévez, Carl Wheezer and his robot dog Goddard. He and Cindy Vortex usually have a dislike for each other, although it is revealed in later episodes that they secretly love each other. In addition to his parents, several of his other relatives have also appeared on the show.

Carl Wheezer Carlton Ulysses "Carl" Wheezer (voiced by Rob Paulsen in the film and TV series and Wally Wingert in the 2002 PS2 and GameCube game) is a bespectacled, neurotic, and gullible boy and one of Jimmy's best friends. Carl and his parents have numerous allergies, at times even to things that are incapable of triggering allergic reactions. He passionately loves llamas, hanging posters of them throughout his room and playing llama-themed video games. His passion for llamas is often used as a running gag throughout the series. In later episodes, until knowing Elke and falling in love on her, his apparent crush on Jimmy's mom was a running gag, and he sometimes taped his own face over Hugh's in pictures. Since the episode "Carl Wheezer, Boy Genius" he knowed the swedish girl Elke Elkberg and falled in love on her. An extraterrestrial character named Doppy, with many similarities to Carl, is a main character in Planet Sheen.

His extreme unhealthy obsession for the llama originated when his parents expanded their cable lineup and he became devoted to a show called Llama Boy The Super Hero that aired on a channel dedicated to the animal. Since his obsession with llamas began, he has gone to great lengths to express his love and care for them, going as far as to join a fan club called The Llama Love Society, which he likely created himself.

It is worth noting, Carl is afraid of lima beans, germs, and scary stories. He is also known to have asthma and uses an inhaler, and he is very stressed about his multitude of allergies and is extremely terrified of getting any sort of illness, similar to his parents. Also, when he is tired, his mom makes him warm milk, rubs his tummy, and sings "nani nani nani", which he blurts out in an episode.

A recurring gag throughout the series is Carl singing melodramatic ballads about mundane tasks, such as "Folding and Hanging", "Bending and Stretching" or the self-referential "Sitting and Singing".“Jimmy Neutron / Dream of Jimmy.” Season 1, episode 05.Steven, Banks (July 20, 2002). "When Pants Attack". The Adventures of Jimmy Neutron, Boy Genius. Season 1. Episode 1. Nickelodeon. "Jimmy Neutron/Attack of the Twonkies" Season 3. Episode 1. Nickelodeon.

Sheen Estévez Ramón Juarrea "Sheen" Estévez (voiced by Jeff Garcia) is a Mexican-American boy and Jimmy's slightly older, hyperactive, addled best friend, characterized by his unhealthy obsession with the fictional superhero "Ultra Lord" and the television series, video games, and merchandising inspired by the character. Sheen lives with his father, sister, and grandmother. Sheen's father makes a brief appearance in season one, though his face is not shown.

Sheen is noted for his extreme, constant bouts of hyperactivity, which he demonstrates multiple times per episode, along with his misdirected, limited intelligence and short attention span, much to the annoyance of his peers. Alongside UltraLord, Sheen also appears to be interested in superheroes in general and in typical masculine subjects such as wrestling and is strongly infatuated with Libby, becoming her boyfriend by the time of the program's conclusion.

Sheen stars in the spin-off series Planet Sheen, which premiered in 2010. In the series, Sheen is stranded on the planet Zeenu after sneaking into Jimmy's lab and stealing his new rocket ship, which blasts him into space. He is never shown returning to Earth. However, in the episode "The Tomorrow Boys", Sheen is shown to be living on Earth in the future.

Sheen was conceived as Japanese-American, but his ethnicity was changed to Mexican-American after Jeff Garcia portrayed him this way during auditions since other voice actors who were considered for the role struggled to give him a Japanese-type accent. His full name is a reference to the last names of both stage names and real names of father-son actors Martin Sheen, Charlie Sheen, and Emilio Estévez.

Cindy Vortex Cynthia Aurora "Cindy" Vortex (voiced by Carolyn Lawrence) is a blonde-haired girl who lives across the street from Jimmy's house. She is a very sarcastic and independent tomboy who enjoys tai chi and karate and will do anything for attention. She is also very smart and achieves the highest grades in her class besides Jimmy, a point of competition and dislike between the two of them. She feels that Jimmy is only ahead of her because he was given the better lot in life, and envies his lab. Despite frequently talking down to Jimmy and labeling him a "nerd", she herself is not popular with many people aside from her best friend Libby. She has always had a crush on Jimmy, but because of her pride it takes a while for her to admit it. In seasons 2 and 3, Jimmy and Cindy are placed in multiple situations where they need to work together, causing them to eventually come to terms with and realize their affection for each other. She often serves as an antagonist, but Jimmy also considers her part of his friend group.

Libby Folfax Liberty Danielle "Libby" Folfax (voiced by Crystal Scales) is a popular-styled African-American girl who is known as the "cool girl" of the team and at the school and Cindy's best friend who is a dancer and especially adores, funk music, emo rock, and boy bands. Early in the series, Libby does not care very much for Jimmy and his friends, often siding with Cindy, but as the series continues, Libby becomes more attached to Jimmy, Carl, and Sheen. In the episode "Beach Party Mummy", Libby takes on a braided bob hairstyle while posing as the Egyptian queen Hasabataslapya, and maintains this hairstyle for the rest of the series. After Sheen professes his crush to her in "Love Potion 976/J", Libby takes a romantic interest in him.

Libby's father appears in the episodes "Make Room for Daddy-O", "Men at Work", and "Win Lose and Kaboom", and makes cameo appearances in several other episodes. Libby's mother appears in "Journey to the Center of Carl" and "The N-Men".

Goddard Goddard (voiced by Frank Welker) is a robotic dog, invented by Jimmy. He is loyal to his owner and often accompanies him on his adventures, including to different planets. Jimmy has programmed Goddard to arrive when called via Jimmy's phone. Goddard has various features including self-propelled flight, storage, and a rocket propelled bicycle-like transportation, complete with handle bars. Jimmy often uses Goddard to help weigh options for his dilemmas, which Goddard displays on a computer monitor that is normally covered by his breastplate. He has mostly the disposition of a normal dog, but occasionally uses voice clips to communicate. Jimmy can have Goddard "play dead", which causes him to self-destruct and instantly reconstruct his body without assistance. He is named after physicist Robert H. Goddard.

Hugh Neutron Hugh Beaumont Neutron (voiced by Mark DeCarlo) is Jimmy's father and Judy's husband. He is portrayed as a happy-go-lucky, duck-obsessed, clueless, dimwitted, but good-natured man who works in an automotive assembly plant. He frequently offers advice to Jimmy in an attempt to be a better father. Ducks are Hugh's favorite hobby; he enjoys collecting and buffing duck decoys, displaying them around the house. The character is named after actor Hugh Beaumont, who played Ward Cleaver in Leave it to Beaver. His voice was in part an impression of one of the series producers, Paul Marshal.

Judy Neutron Judith "Judy" Neutron (voiced by Megan Cavanagh) is a homemaker and baker, Jimmy's mother and Hugh's wife. She is a responsible parent for her son Jimmy, and often takes on a similar role for her husband Hugh. She addresses Jimmy by his full name whenever she scolds him or one of his inventions messes up. Regardless, she has stated that she appreciates her union to Hugh and is happy in their marriage.

Supporting

Ms. Fowl Ms. Winifred Fowl (voiced by Andrea Martin) is the teacher for Jimmy and his friends, who both resembles and, when speaking, frequently squawks like a chicken, hence her surname.

Nick Dean Nicholas "Nick" Dean (voiced by Candi Milo) is a Asian-American boy and the "cool" and most popular boy at school who is often seen on a skateboard, doing dangerous tricks. He does not participate in his school's show and tell activities and sometimes arrives at school five minutes before dismissal. Nick is obsessed with styling his hair, and is considered very handsome by all girls in the school. Nick is one of the town's wealthiest children, living in a 92-room mansion, with a bowling alley, maids' quarters, a screening room, and a soda parlor.

UltraLord UltraLord (voiced by Jim Cummings in the film and TV series and Rob Paulsen in the PC 2001 video game) is a superhero for whom Sheen has an unhealthy obsession and who stars in a TV series of the same name. His main enemy is Robo-Fiend. Sheen has the largest UltraLord action figure collection and is offended when other characters call them "dolls".

Butch Pakovski Butch (voiced by Billy West in the film and Rob Paulsen in the TV series) is a slightly slack jawed bully. Butch may have a softer side as he is seen in one episode clearing his anger with stacking sticks. In the beginning of the episode "Jimmy Goes to College", Jimmy uses sophisticated words to describe his unstable molecules and Butch holds his head, saying "Big words! They hurt! They hurt!".

Mr. and Mrs. Wheezer