James "Jimmy" Isaac Neutron is the main protagonist of the Jimmy Neutron franchise and a supporting character of the French Disney show, The Life and Times of Elmyra Howard. He is the leader of the Neutron team, his counterpart, male boyfriend of Cindy and the twin brother of Timmy Turner. Jimmy is a genius inventor, but his inventions often cause problems and usually depends on him and his friends to stop them. He lives in Retroville with his robot dog, Goddard and his parents Hugh and Judy Neutron.
Jimmy has an I.Q. of 210, making him the smartest Retroville citizen and, possibly, one of the few smartest individuals in the world. He specializes in many sciences such as quantum physics, chemistry, biology, mathematics, robotics, engineering and astronomy. In several episodes, his classmates are upset and angry because Jimmy's brilliance makes trying to win science projects and competitions meaningless. In fact, Jimmy has been excluded from the science fair for life to give normal children an actual chance to win. His brain, source of constant comments, allows him to invent devices that achieve even the impossible. That may seem like a gift to most people, but for Jimmy, it often causes problems. Though he often uses his inventions for selfish purposes, Jimmy is still a kind and heroic young man.
Jimmy appears as a 16-year-old after finding a mirror to a high school setting.
Jimmy is first seen in the series in the episode "An Apologetic Vengeance", when Phineas, Ferb, Dipper, and Mabel are seen chatting with him on Skype, along with Timmy Turner and Tommy Pickles, to get advice on whether or not to forgive Caillou for his notorious acts in "Off to the Falls". They suggest that they give him a chance and end the chat from there.
In the next Season, Caillou and co. head to Retroville to seek the help of Jimmy Neutron, who happens to be one of the 3 components needed to save Perry from the possession of Bill Cipher. However, they don't go straight to Retroville. Instead, they meet him at the Stadium Theater, where Jimmy is watching a play with his friends. After a weekend of making funny videos and celebrating Mother's Day, Jimmy receives a call from Jet Fusion, saying that Professor Calamitous and Beautiful Gorgeous have broken into the Coast Guard base, with plans to use their technological systems to make a giant wave big enough to flood the entire world. After Caillou and co. help Jimmy and his friends stop Calamitous, Jimmy joins their journey to assemble the heroes.
Jimmy is a 14-year old boy with fair skin, blue eyes, a large forehead, and brown hair in the shape of an ice cream sundae. He later wears a midriff red t-shirt with his trademark yellow atom symbol on it, blue jeans with cuffs, and white converse sneakers. In the movie, he wore blue shorts and brown loafers, as well as keeping his trademark shirt, which is replaced by a red and white striped shirt in the pilot.