- Betty Quinlan
- Bolbi Stroganovsky
- Brittany Tenelli
- Butch Pakovski
- Carl Wheezer
- Cindy Vortex
- Hugh Neutron
- Jimmy Neutron
- Judy Neutron
- Libby Folfax
- Ms. Fowl
- Nick Dean
- Principle Willoughby
- Sheen Estevez
- CategoryGrim Reaper
- Dorkus Aurelius
- CategoryRobot Dog
- Professor Finbarr Calamitous
Britney is a cheerful and lively girl, known for her kind and bubbly personality, cute appearance, and occasional clumsiness. This starkly contrasts with the smart and assertive Cindy Vortex and the sassy Libby Folfax, making her an amusing foil to them. Despite her positive attitude, Britney can be easily confused, as she tends to have her head in the clouds.
She is a highly intelligent and confident girl who often clashes with the show's titular character, Jimmy Neutron. Cindy is known for her quick wit and sarcastic sense of humor, which she uses to assert her dominance and prove her superiority over others. She is also a skilled athlete and martial artist, and is not afraid to stand up for what she believes in.
Throughout the series, Jimmy's exceptional intellect often causes tension with his classmates, who become jealous of his knowledge and abilities in math and science. Despite this, Jimmy uses his intellect to invent a wide range of advanced devices and technologies, often accomplishing what others consider impossible.
She is depicted as a loving and caring mother to her son, Jimmy, and a devoted wife to her husband, Hugh. While Judy is affectionate towards her family, she often becomes frustrated with Jimmy's mischievous behavior and the trouble he causes. In these instances, she will sometimes lecture him or take steps to discipline him.
She is a teacher at Jimmy's school and is known for her odd behavior, eccentric personality, and quirky mannerisms. Ms. Fowl is often depicted as being absent-minded, forgetful, and a bit strange, with a tendency to go off on tangents during class. Despite this, she is generally well-meaning and is dedicated to teaching her students.
Despite his initial behavior, Nick is a character who possesses both negative and positive qualities. He has been observed to act like a jerk, exhibiting traits such as pessimism, arrogance, snarkiness, and cynicism. However, beneath this exterior, Nick has a kind and compassionate heart.
He is one of Jimmy's best friends and is known for his hyperactive and impulsive personality. Sheen is portrayed as being highly energetic and often gets overly excited about the latest trends or gadgets. He is also shown to have a strong interest in outer space and aliens, and is a self-proclaimed "ultra Lord" fan, a popular sci-fi show within the show's universe.
Mr. Nesmith is a character whose appearance is described as having a brown and tanish color. He has unique features such as white eyes with black pupils, gray boots, and a red hat. His spacesuit is predominantly white with blue and red lines, and a depiction of the planet Saturn on it. Mr. Nesmith also has brown arms, a peach-colored nose, and two ears.
He is a mad scientist and inventor who frequently plots to take over the world using his various inventions and technologies. Calamitous is known for his evil and diabolical nature, as well as his cunning intellect and strategic planning. He is also shown to be highly manipulative, often using others to achieve his own goals.