This is a list of characters from the animated Nickelodeon TV series Jimmy Neutron. The recurring cast includes long-term Nickelodeon voice actors Debi Derryberry.
- James Isaac "Jimmy" Neutron is the main protagonist of the show. He is an 11-year-old American boy with a stunning IQ and a love for science. Usually, his inventions cause more harm than benefit for the city of Retroville, but that never stops him from trying. Most of the time, he's busy saving the city from his own experiments gone wrong. He is best friends with Carl and Sheen. Throughout the series there are hints that he has feelings for Cindy Vortex, although he is in love with Betty Quinlin. His middle name is named after Isaac Newton, the famous physicist voice by Debi Derryberry.
- Hugh Neutron, Jimmy's father. Somewhat oblivious and childish. Likes pie and ducks. He loves it when his "sugar-booger", Judy, makes him waffles that resemble faces, usually ones that represent how she is feeling. He also likes every fast-food restaurant with the exception of McSpanky's (the restaurant where Jimmy and his friends were working at in the episode Men at Work; an obvious reference to McDonald's.), possibly because he almost became a millionaire by investing in the restaurant, but chose against it. He is the only adult who goes to the Candy Bar on a regular basis, except Sam, who runs the place. He is well known for playing with (and misusing) Jimmy's gadgets. He also invented the holiday Pule.Voiced by Mark DeCarlo.
- Judy Neutron, Jimmy's mother. Most likely where Jimmy gets his brains. Judy appears slightly more mechanically inclined than Hugh (as shown in the original movie when she repairs the family car). She is a neat freak and when angry, calls Jimmy by his full name, James Isaac Neutron. She is called "sugar booger" by Hugh. Carl Wheezer is in love with Judy Neutron, noted in various episodes. Her outfit resembles a 1950's housewife. Voiced by Megan Cavanagh.
- Goddard, Jimmy's robotic dog, equal parts tool and friend. Goddard can, according to Jimmy's dad, Hugh Neutron, do eleven million and four things with the exception of cleaning up his own droppings (made of nuts and bolts). Along with the ability to shoot out laser beams he has, among other things a built in ray gun, lie detector, sound system, satellite radio, computer and clock. He can also change into a flying motorcycle. Goddard is portrayed as having the habits of a regular dog with the exception of his diet of metal and that when told to play dead he self destructs in a main core implosion (only to rebuild moments later). This was a flaw that Jimmy made a feature after finding its usefulness. Voiced by Frank Welker.
- Carlton "Carl" Ulysses Wheezer, Jimmy's neurotic, llama-loving friend. According to canon, Carl was born in 1991. Carl is known as nervous, timid and suffering from hypochondria; at times, he tries to overcome these personality traits in order to appear "cooler" around Jimmy and mutual friend Sheen Estevez. When his parents expanded their cable lineup, Carl found himself focusing on a channel devoted to llamas; he has adored them ever since, going so far as to join a fan club, the Llama Love Society. Has an odd taste in women and an even stranger crush on Mrs. Neutron. Voiced by Rob Paulsen.
- Sheen Juarerra Estevez, Jimmy's hyperactive friend, is twelve years old, making him two years older than Jimmy and Carl. The three are in the same school grade because Sheen was held back. Sheen's wardrobe largely consists of a blue t-shirt and jeans. The t-shirt depicts UltraLord, a popular superhero within the show that Sheen is obsessed with. Sheen is of Mexican ethnicity, but does not have a noticeable accent. The name "Sheen Estevez" appears to be a reference to the Estevez family of actors — specifically the two members, Ramón and Carlos, who use the screen name Sheen (Martin and Charlie Sheen, respectively). Voiced by Jeffrey Garcia, who also won an Annie award for the role.
- Cynthia "Cindy" Aurora Vortex, Jimmy's rival. Has shown obvious but reluctant friendship toward Jimmy. Usually calls Jimmy Nerdtron or some other such name.In the hour long crossover special, Jimmy Timmy Power Hour, Cindy develops feelings for Timmy Turner. As admitted by director Keith Alcorn and writer Steve Marmel, Cindy will end up with Jimmy in the long run. She loves Jimmy and only likes Timmy.
- Liberty "Libby" Danielle Folfax, Cindy's best friend. Somewhat intellectual, and obsessed with electronic gadgets. Also Sheen's girlfriend, by some twist of fate. Libby, was often referred to as "The Music Lover" and "Cindy's Best Friend", until the episode "Beach Party Mummy", when she really came out of her shell, as well as changing her look.She is pretty intellectual, loves electronic gadgets, and is related to Egyptian Queen Hazabataslapya (pronounced "Haws-Abut-ay-Slap-Ya), as seen in the episode "Beach Party Mummy", where she received a brand-new hair makeover to look like the Queen of the Nile, which she still has. She's 11 years old. Libby listens to only the funkiest music. She can play the piano as seen in My Big Fat Spy Wedding. She mostly returns Sheen's interest in her, but only when he's not annoying her with his overbearing mentions of Ultra Lord and his occasional flirting. Libby sometimes joins Cindy in teasing Jimmy, but has full knowledge (and may have been the first to notice) that Cindy and Jimmy love each other. She has a little brother, who appeared in the Father's Day episode, "Make Room for Daddy-O".
Voiced by Crystal Scales.