This is a list of characters in the American film Jimmy Neutron: Boy Genius and the television animated series spin-off The Adventures of Jimmy Neutron: Boy Genius.
Voiced by: Debi Derryberry
James Isaac "Jimmy" Neutron is a highly intelligent 10-year-old (later 11 in season 2, 12 in season 3) boy who uses scientific knowledge and inventions to solve issues he is confronted by (most of which he causes himself). He is the son of Judy and Hugh Neutron. His best friends are Sheen Estevez, Carl Wheezer, and his robot dog Goddard. Cindy Vortex is his most important rival, but he secretly feels attracted to her. Jimmy is usually seen wearing a red shirt with his trademark atom symbol on it, blue jeans, and white shoes, sometimes blue shorts and brown shoes. However, in scenes where he's going to bed, in bed, or getting out of bed, he is barefoot and shirtless, wearing nothing but red and orange plaid boxers. While having a sleepover in Carl Weezer's house, he wears a white shirt with a yellow atom on it just like his red shirt. He has blue eyes and brown hair that is considered "anti-gravity" and is in a whipped-up form, earning him many nicknames from classmates (especially Cindy), such as "Whippy-Dip" from his clone Evil Jimmy, and "Señor Fudge-Head" (from Cosmo in The Jimmy Timmy Power Hour).
Voiced by: Jeffrey Garcia
Sheen Estevez is Jimmy's slightly older, hyperactive, addled best friend, characterized by his unhealthy obsession with the fictional superhero "UltraLord" and the television series, video games, and merchandising inspired by the character, collecting all of the memorabilia related to the superhero that he can-even going so far as to write an entire website dedicated to UltraLord and also wears his trademark UltraLord T-shirt. Aside from his dedication to UltraLord, Sheen is noted for his extreme, constant bouts of hyperactivity which he demonstrates multiple times per episode, along with his misdirected intelligence and short attention span, 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 Folfax, becoming her boyfriend by the time of the program's conclusion, and lives with his father and grandmother.
Sheen would later star in his own spin-off show, Planet Sheen. In this series, he sneaks into Jimmy's lab and steals his new rocket ship, which crash lands him onto the planet of Zeenu. Due to the series being short-lived, he is never shown returning to Earth. However, it is implied in "The Tomorrow Boys" that Sheen did return home. (Note: His full name is a pun on the last names of both stage name and real names of father-son actors Martin Sheen, Charlie Sheen, and Emilio Estevez.)