- "Gotta blast!"
- ―Jimmy's catchphrase.
Jimmy is a genius inventor, but his inventions often cause trouble and it is usually up to him and his friends to stop them. He lives in Retroville with his robot dog, Goddard and his parents Hugh and Judy Neutron.
Jimmy is an adorable 12-year old boy genius with a large forehead (which appears to be larger, due to his hair), blue eyes, and a large brown cowlick ice cream sundae-shaped hairstyle. He is often teased because he is shorter than most of the kids his age and one of the youngest students in his class.
Jimmy's wardrobe consists almost exclusively of red T-shirts that sport his famous yellow trademark symbol of an atom. He also wears blue jeans and a pair of grey and white Converse sneakers. His underwear consists of plaid boxer shorts, as shown in the film and in the first episode of the series. He wears also wears a pair of white socks. In the shorts and the film, Jimmy wore violet-blue shorts and brown shoes with white laces. He also wears a light blue lab coat (and sometimes his welding mask while working on his inventions). Whenever he goes to bed, he wears blue and red pajamas or a white variant of his regular shirt.
In the pilot, he wore a striped shirt with his brown loafers and blue shorts. A picture of him in this outfit can be seen several times in the show.
Jimmy has an impossible I.Q. of 210, making him the smartest Retroville citizen and quite possibly the smartest individual in the whole world. He specializes in many sciences such as quantum physics, chemistry, biology, mathematics, robotics, engineering and astronomy. In a number of episodes, his classmates are annoyed and angered because Jimmy's brilliance renders trying to win science projects and competitions things pointless. In fact, Jimmy has been banned from the science fair for life to give normal kids an actual chance. His brain, a source of constant comment, allows him to invent devices that accomplish even the impossible. That might seem like a gift to most people, but to Jimmy, it often causes him trouble.
He designs his wild inventions to help him deal with bothersome chores, play tricks on people and gets very curious when there's something unusual happening, however the inventions tend to have a flaw (usually caused by an obvious oversight) and his curiosity can take over him, which results in a catastrophe which only he can solve. He's rarely ever thanked however as people usually know the problem was his fault in the first place and is highly considered a menace by everyone. The whole point of this is to show us that while Jimmy is a genius, he's still a kid and acts his age.
In the moment of crisis, he will urge his brain by saying, "Think, think, think!", where upon viewer enters Jimmy's ear and goes into his brain to observe its inner workings as well, as to relive a scene from the early part of the episode. Jimmy will then shout, "Brain Blast!", and arrive at the solution for whatever danger he has landed himself, his friends, or his town in. In the movie, he does not say "Think, think, think!" or "Brain Blast!" out loud, but says them in his mind. In the third season, he seems to stop brain blasting and comes up with ideas right away, with the exception being "Fundemonium".
Jimmy is a very nice guy, although sometimes he can be arrogant, selfish, irresponsible and a know-it-all. Jimmy is shown to be quite irritable and impatient around most people, mostly his friends and sometimes treats them like underlings. He can be friendly, but can come off as a smart-aleck or a nerd and sometimes he can be unsympathetic to people's feelings. Sometimes, he makes up scientific claims, which his friends think are a bunch of baloney. Jimmy is also shown to be lazy in several episodes and relies on his inventions to do even the simplest things for him, which causes trouble for him and everyone around him. Jimmy also almost never learns from his mistakes and usually doesn't listen to his friends when they try to warn him about something in his plans. He enjoys being a hero, often taking a staunch stand against anyone he believes to be evil. He won't back down from his beliefs and he strongly believes in himself.
Jimmy is quite charming when he least tries to be, such as at the party that he lets Sheen throw in his parents' absence in an early episode. He cares deeply for his friends, parents and Goddard. It shows that Jimmy's intelligence is not inherited from the father, but he took it from his mother, conversely from his father Hugh, who is a duck-obsessed adult.
In a few episodes, Jimmy is shown to be somewhat gullible and throughout the series, he loses his common sense and doesn't think his inventions and plans through. Despite all this, he nearly never learns from his mistakes and refuses to acknowledge them.
Sometimes though, it is hinted that Jimmy may, deep down, be insecure about being super smart, as he is constantly bullied because of it and that he causes problems for everyone, indicated by his statements in Normal Boy. He is also shown to be insecure about his small stature and loses his temper when he's mocked or reminded of it. He is also hinted to be lonely a few times.
There are times when Jimmy actually shows signs of humility and actually takes responsibility for his actions. A perfect example would be in the movie, when he realizes that the parents getting abducted was his fault and his friends become bitter towards him. In his own separate cell, Jimmy starts crying, not just out of remorse, but out of his own insecurities.
In the shorts and the movie, Jimmy was portrayed as awkward, naive, clumsy, a bit child-like, nerdy and shy and his voice was also a bit more high pitched and scratchy. However, in the show and for the rest of the franchise, he has become more of a leader, a bit irritable, kind of a know-it-all, somewhat arrogant and his voice is more deep and clear.
However, he does have a few weaknesses; one of them is his poor communication skills. It takes him hours to explain things the scientific way and people find his explanations very complicated and would ask for a shorter version of his story instead, leading some fans to believe he might have a case of Autism, which is quite common in science nerds. Cindy calls him silver-tongued in the episode "Love Potion 976/J", as he finds it hard to express his feelings.
In the episode, Lights! Camera! Danger!, Jimmy is revealed to be a terrible artist and writer due to his lack of creativity, since he's a math and science prodigy. But in the movie, he can draw fairly well, as far as his inventions' blueprints are concerned.
He creates a lot of his inventions in his lab, which is accessible to him only, by means of a DNA scan from his hair. Jimmy's inventions include, but are not limited to Goddard, a time machine, the Nanobots, and many more. He has several gum and candy-based inventions, which include The Neutronic Air Gum, that allow humans to breathe under water, gum that allows one to memorize books, and candy, that satisfies all the tongue's taste buds. After eating such candy, humans develop a physiological need (addiction) for it. He also made inventions to help him with transportation, the most frequently employed being his flying rocket or hover car. He also has a game pyramid, which allows players to go inside their favorite video game, and a Cloning Machine.
Jimmy also has a watch that is able to communicate with others, thought it is not clear when he invented (or enhanced) it.
In the video games, he makes several inventions out of old junk. Many times, he creates different types of advanced spaceships with space buses, space bikes, being able to use amusement rides to create some, and finishing with his favorite, the hovercar, which he uses almost frequently. He creates these inventions in an extensive lab, located under his clubhouse, which is accessible to him only, by means of a DNA scan from a piece of his hair.
In the Chrysler Town & Country Commercial, he introduces his newest invention: "The Neutron Dimensionalizer."
One of Jimmy's best friends is the llama-obsessed Carl Wheezer. Carl may not be as smart as Jimmy, but he is very loyal to him. He's willing to help Jimmy as much as possible, but hates testing Jimmy's inventions. Normally, he plays the foils to Jimmy's genius and sometimes solve the episode's crisis with some innocent or insane observation. However, other times, he is the cause of the problem. He accompanies Jimmy in his wild adventures and usually ends up in trouble. Jimmy likes Carl because he is loyal and helps Jimmy with his experiments. The two usually share good chemistry.
Another one of Jimmy's best friend is the hyperactive Sheen Estevez who is obsessed with Ultra Lord. Sheen is responsible for a great deal of the blunders Jimmy often has to fix. He also volunteers to test Jimmy's experiments, but not nearly as often as Carl. Like Carl, he is not near as smart as Jimmy. In Sheen's Brain, Jimmy uses the Brain Drain Helmet to make Sheen a genius like him, which causes his brain to increase in size (and even becomes smarter than Jimmy); he also gains telepathic abilities and telekinesis and plots to destroy the town. When Sheen brutally strikes Jimmy and Carl with a lightning bolt, he realizes that his new powers have turned him into a monster and changes back to normal before the danger of his head exploding occurred. They usually share good chemistry.
Goddard is Jimmy's best friend and without a doubt, his favorite invention. Jimmy and Goddard clearly have a "boy and his dog" relationship and Goddard is always there to help Jimmy when he's in trouble. Jimmy cares deeply for Goddard and gets emotionally crushed when he gets hurt or loses him. Even during Jimmy's toughest challenges, he has always been able to rely on Goddard and always be there for him no matter what. The two share great chemistry.
Main article: Jimmy and Cindy's relationship
Cindy is Jimmy's female counterpart and girlfriend. When Cindy moved into town, Jimmy was no longer the only genius in town and they became fierce rivals. Even though they bicker frequently, Jimmy stills sees Cindy as a friend because she is the one person who keeps him on his feet and Cindy doesn't like it when Jimmy is sad or heartbroken and always goes to comfort him. They grow to admire one another, and even develop crushes on each other over the course of the series, but act as if they dislike each other in front of others in order to hide it. They begin to secretly go out on dates towards the end of the series and pretend to fight for the sake of their reputations. Their chemistry often varies depending on the episode.
Jimmy likes Libby because she is calm, mellow and sensible. Libby plays a big sister role to Jimmy and is always trying to get him to come out of his shell, which Jimmy often reluctantly agrees to. In Crouching Jimmy, Hidden Sheen, when Yoo-Yee kidnaps Libby, he works hard to help Sheen fight him to save her. Jimmy and Libby's chemistry is rather good.
While Jimmy and Nick don't hang out as much as they did in the movie and season one, Nick plays a big brother role towards Jimmy. He usually gives him advice, just not very good advice, advice which sometimes gets him in trouble. Nick does tease Jimmy sometimes, and sees him much like an annoying little brother, but they are very good friends and have a strong bond. If season four had happened, Nick would have rejoined the main cast and further developed his relationships with Jimmy and the other main characters. The two share good chemistry.
While Jimmy and Brittany don't hang out much, they do get along well and are good friends. The two appear to have a brother-sister relationship. Jimmy likes Brittany because she's sweet, innocent, kind and she is one of the only people who doesn't antagonize him and that she's one of his very few fans. Sometimes, it is hinted that Brittany might have a crush on Jimmy. They share great chemistry.
Main article: Jimmy and Betty's Relationship
Betty Quinlan is Jimmy's first crush and another one of his best friends. Jimmy very noticeably displayed affection toward her, even in front of his peers. He always hid his crushes from people in other instances, which shows that his crushing on Betty was strong enough that he showed it without realizing it. He often tried to impress her with his inventions, and she seemed charmed by him. She flirted with Jimmy thoughout the series, seemingly aware of Jimmy's interest in her. Towards the end of the series, she began to pick up on Jimmy and Cindy's growing feelings in each other and she seemed fully supportive of it, although it is hard to show it because Cindy is always mean to her. Jimmy and Betty do remain friends, however. They have good chemistry.
However in League of Villains, it is shown that Jimmy still has a drawer full of pictures of Betty in his lab, and he had one sitting out by his computer and one in his captain's log. Though Cindy made him get rid of them, this makes it clear that Jimmy still likes her.
Jimmy has a strong and loving relationship with his parents, Hugh and Judy. They are always there for him when he needs them, although they do get annoyed with Jimmy's rebellious and mischievous behavior, and the trouble he and his inventions cause. They are loving parents, correcting his misbehaviour, while still supporting him and caring for him.
Sadly though, Hugh and Judy seem to be the only relatives who care about Jimmy, since his other relatives (on Hugh's side at least) consider him a black sheep for being different, as shown in Clash of the Cousins.
- "Gotta blast!" - Jimmy's catchphrase
- "Think, think, think! Brain Blast!" - Jimmy's catchphrase
- "Pukin' Pluto!"
- "Gas planet!"
- "Leaping leptons!"
- "Holy Heisenberg!"
- "Jumpin' Jupiter!"
- "Very Capable Robots!" -??
- "I already told you Goddard, this invention helps me bring down my ego when Cindy calls me a 'know-it-all'. It's hard to not act like a know-it-all when you actually do know it ALL." - Substitute Creature
- "Twenty-five cents?! I'm worth at LEAST-" - Birth of a Salesman
- "Hmm... The candy is so perfect, it seems to have developed a physiological need in people. Let the exploitation begin!!" - Krunch Time
- "I hereby accept your nomination as mayor of Donkey Town." - Stranded
- "I'm sorry, miss. Do I know you?" - Normal Boy
- "Ha! Just kidding! Let's PARTY!!!" - The Eggpire Strikes Back
- "No, but we survived by learning to help each other, and that's what makes us rich: rich in friendship!" - A Beautiful Mine
- "(Goddard shows on screen)...Go back in time and tell Cindy you will lose the contest.' Jimmy: Goddard, whose side are you ON?!!..." - Birth of a Salesman
- "This is going to be a memorable Halloween Goddard. That is if we survive." - Nightmare in Retroville
- "That's a nice story, girls, but as it stands, I'M WINNING THIS CONTEST!!!" - Birth of a Salesman
- (Jimmy talking to Cindy) "I can't talk, I can't think. Everywhere I go, you're there!"
Cindy: "What kind of sick joke is this?"
Jimmy: "Oh, you're gonna make me say it, aren't you? Okay, then, I'll say it..... I love you, Cindy Vortex!" - Love Potion 976/J
- "I've developed a plan in case the ninjas return." - Crouching Jimmy, Hidden Sheen
- "I'm dead! I'm streaking, and I'm dead." - Jimmy Goes to College
- (Goddard shows on screen) "'Cheat'... Cheating would be dishonest... But I'm too blinded by my desire to beat Cindy to care!!" - Maximum Hugh
- "Gentlemen, I give you the Brain Drain 8000. The same dumbing down technology used by top radio personalities." - Normal Boy
- "I may have made a tiny miscalculation...!" -Jimmy on Ice
- "By the way, the guys told me about the Candy Bar. I'm afraid I'm gonna have to erase your short term memory." -The Eggpire Strikes Back
- "I hate where this is going..." -Attack of the Twonkies
- "Um, Cindy, I know you've been through a lot the past few hours, but, um... Get OUTTA MY LAB!!!" -Jimmy Timmy Power Hour
- "Gentlemen, I give you: our UltraLord thief!" -Crime Sheen Investigation
- "Don't, Sheen! That's highly concentrated essence of sour!!" -Krunch Time
- "I can't maintain top speed! My rocket must've been damaged when it landed! Wonder who was driving?!" -The League of Villains
- "A striped moon?! That's a meteorological impossibility!!" -Win Lose and Kaboom!
- "What's wrong with you guys?! You've been fighting ever since we got rid of those stupid bandits!" -A Beautiful Mine
- "If you think you can do a better job, then just SAY SO!!" -Win Lose and Kaboom!
- "Me see you soon day!! ...'Me see you soon day'?! What a stupid thing to say! Wait, why should I care what Cindy thinks? And why did I get lost in her limpid green eyes?! I've been in the lab too long!" -Love Potion 976/J
- "I'll tell you what's clear: you're a loony old boat jockey with salt on the brain!! And I'll tell you what else! This voyage is OVER, unless someone can explain, in the next ten seconds, how a giant, reptilian monster could POSSIBLY exist in a manmade, freshwater ecosystem!!!" -Monster Hunt
- "Run, Cindy, run!" -One of Us
- "You're going back to the lab and I'm going to declone you!" -Send in the Clones
- "Uh, Sheen, ya might wanna hold off on the taunting for just a few more minutes...!" -Sorry, Wrong Era
- "Right about... (points) there... Long-range space scanners have detected the ion trails, indicating the departure route left by whatever alien intelligence has abducted our parents. And as you can see, they lead us to somewhere in the Orion star system approximately three million light years away... So that means we'll have to leave by Friday. Okay, that gives us two days to collect the necessary plutonium, design and test our fusion engines, and build our fleet of interstellar warships. We'll also need to bring snacks! Any questions??" -Jimmy Neutron: Boy Genius
- "Science, shmience! Run for your lives!!!" -The Phantom of Retroland
- "What is that bewitching scent?" -King of Mars
- "Leapon Leptons! What happened to Sheen's head!?" -Sheen's Brain
- "You scrambled up my dog's atoms and let a girl in my lab!? What kind of genius are you!?" -Jimmy Timmy Power Hour
- "They used my Re-generator to make a brand new Poultra!" -The Eggpire Strikes Back
- "RUN, GODDARD!" -Billion Dollar Boy
- "I don't understand it! I was only trying to boost his IQ so he'd pass the math test!" -Sheen's Brain
- "It's Poultra, get back! The Yokians are more evil then ever! RUN FOR YOUR LIVES!" -The Eggpire Strikes Back
- "You're going down, Turner!" -Jimmy Timmy Power Hour 3: The Jerkinators!
- "Goddard's been dognapped!" -Professor Calamitous, I Presume
- "Nobody steals my dog!" -Professor Calamitous, I Presume
- "Hello, Spongebob, we haven't met, but believe me, I'm your friend." -Nicktoons Unite!
- "You had your fun, Sheen, now let us go!" -Sheen's Brain
- "That's Ms. Fowl!" -Best in Show
- "Well, the computer heard my Dad saying he prefers Taco Shack and now it's off to correct the problem." -Men at Work
- "DAD, NO!" -Men at Work
- "Carl, stop! It's not a game!" -Ultra Sheen
- "My Girl-Eating Plant! It's grown to the size of a building!" -Nicktoons: Globs of Doom
- "Every villain that I've ever defeated has banded together to get rid of me for good!" -The League of Villains
- "Goddard, I'm going to Dimmsdale!" -Jimmy Timmy Power Hour 2: When Nerds Collide!
- "No, Carl, you don't understand. Sheen's brain is programmed to keep growing! If we don't get that Brain Drain Helmet on him soon, his head will explode!" -Sheen's Brain
- "Dear Genius, sorry I let you down. You'd be better off with a real dog like everyone said. Signed, your ex-pet Goddard. He ran away!" -Best in Show
- "I'm not doing anything for you, Mr. Calamitous!" -Professor Calamitous, I Presume
- "It can fit all five of us. Plus Goddard." -A Beautiful Mine
- "Come on, Carl, we've gotta stop Ooblar! We're the only ones who can save the Nicktoons, and the planet!" -Jimmy Neutron's Nicktoon Blast
- "There we were, running for our lives from our best friends and family. How did this happen? It all began on a normal day at school." -One of Us
- "People listen to me! It's just candy!" -Krunch Time
- "You can't eat them, Carl. The blue neutrons are energy for my inventions." -Jimmy Neutron: Boy Genius Video Game
- "We'll take the Mark II and you guys could follow us with the Mark I." -Jimmy Neutron's Nicktoon Blast
- "Thank you for coming, you two. For once, I'm really glad to see you." -The Great Egg Heist
- "I really hate that clone!" -The Trouble with Clones
- "You look like me, but you're wearing a fake beard!" -Jimmy Neutron vs. Jimmy Negatron
- In the episode "Grumpy Young Men", he has a head similar to Albert Einstein.
- Jimmy's original name was Johnny Quasar and didn't have his large brown cowlick. They changed his name because it sounded too much like "Jonny Quest".
- In the shorts, pilot and the movie, Jimmy's voice was more scratchy, nasally and higher. In the series, his voice is more deep and clear.
- During the time of the movie and the early years of the show, Jimmy became Nickelodeon's official mascot.
- Jimmy, Carl and Sheen are the only characters to be in every episode of the series.
- In Planet Sheen, Jimmy is mentioned in the pilot when Sheen questions the J.N initials on the notes.
- There was going to be a TV movie about Jimmy and the others going to Zeenu to find Sheen, but due to low ratings, production costs and several writers moving on, the movie was cancelled.
- Jimmy is ten in the shorts and movie, eleven in the first season and twelve for the rest of the series.
- Jimmy and Nick are the only male characters to be voiced by a female. Jimmy is voiced by Debi Derryberry and Nick is voiced by Candi Milo.
- Other voice actors who auditioned to voice Jimmy included Nancy Cartwright, E.G Daily and Pamela Adlon.
- Throughout the show, it is constantly hinted at that Jimmy inherited his intelligence from his mother, who has shown certain degrees of brilliance herself like when in "See Jimmy Run", she explains how the overwhelming speed of the shoes could cause his shoes to meltdown. In fact, in the book Genius 101, he even comments on Judy's cleverness and Hugh's bumbling nature, saying that is quite obvious where he got his intellect. However, in "Clash of the Cousins", Jimmy analyzed the "Neutron genius gene" which actually comes from his father's side of the family. Although, it is a possibility that both sides of the family carry an individual genius gene.
- In the pilot Runaway Rocketboy, Jimmy wears a striped shirt instead of his trademark atom shirt. A photo of him in this shirt can be seen on the staircase often in the show.
- It would appear that Jimmy has Autism, which is quite common in science geeks.
- Sometimes, Jimmy speaks redundantly.
- His hairstyle in Love Potion 976/J and Lady Sings the News resemble Eustace's.
- Jimmy is the only one to appear nude in public.
- Jimmy is also the only character who does not act as an antagonist willingly.
- It has been established several times his birthday is in March, as stated by Keith Alcorn, making him a Pisces.
- As an animation goof throughout the Jimmy Timmy Power Hour trilogy, whenever Jimmy is seen in FOP style, his watch constantly disappears off his wrist.
- Jimmy is the only male member of the gang to have more than one syllable in his name.
Main Characters: Jimmy Neutron | Carl Wheezer | Sheen Estevez | Nick Dean | Cindy Vortex | Libby Folfax | Brittany Tenelli | Betty Quinlan | Goddard