Human
She is one of the students in Jimmy's class at Lindbergh Elementary School and is often portrayed as one of the popular kids in school.
He is a foreign exchange student from an unknown country and is often portrayed as eccentric and clueless, yet extremely friendly and positive. Bolbi speaks in broken English and often mixes up his words, leading to many comedic moments throughout the show.
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.
With a slack-jawed expression and brown hair, Butch is a character whose eyes are covered by a large frontal bang. He has a round nose and appears to be hunchbacked, wearing a purple shirt with a white stripe in the middle, gray pants, and purple and white tennis shoes.
Carl has peach-colored skin with numerous freckles, and is characterized by small black eyes and red hair. Typically, he is seen wearing an orange-and-red-striped shirt, green pants (sometimes with suspenders, as shown in the movie), and glasses.
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.
Hugh is known for his love of ducks and pie, which are recurring motifs throughout the series. Despite his occasional odd behavior, he is a lovable character who adds a lot of humor and heart to the show.
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.
Libby is known for her sassy and confident personality, often providing a counterbalance to Cindy's more studious demeanor. She is a talented dancer and performer, with a flair for fashion and a strong sense of style.
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 the principal of Jimmy's school and is known for his stern demeanor and no-nonsense attitude.
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.
Grim Reaper
With an appearance similar to that of the Grim Reaper, he is draped in a green cloak held in place by a knot. In addition, he is characterized by unkempt fingernails and yellow teeth.
Robot Dog
Goddard is a highly advanced robot, equipped with a wide variety of gadgets and tools that are often essential to Jimmy's inventions and adventures. He is also capable of transforming into a variety of different shapes and forms, such as a jet engine, a rocket, or even a submarine.
Monkey
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.
Scientist
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.