Simon Seville is the deuteragonist of the series and films. He is the smartest of the group, possessing an I.Q. just north of Einstein.
Simon possesses a very dry sense of humor, as well as a keen wit. Simon gets along great with Jeanette, who is smart, just like him. They are shy about their relationship, however it is obvious that he cares for her.
Simon is the smart brother of the three and is seen as the person who values the 'status quo' of action, often correcting his brothers or The Chipettes if he perceives them as wrong. He is the middle child, as revealed in the episode Grounded Chipmunk when Alvin states he has never been alone, except those five minutes before Simon was born. Simon's often seen spending the most time with Theodore and often is working on a science experiment. He wears a long blue sweater and round blue glasses for his attire. His glasses are black in early season of the show and in direct-to-video films Alvin and the Chipmunks Meet Frankenstein and Alvin and the Chipmunks Meet the Wolfman.
Alvin exploits Simon's master mind. In the end, Simon loves Alvin, although he secretly worries that they share the same gene pool. His signature color is blue, and has the same color eyes. He wears black glasses in the live action film. His instrument is the bass guitar. In the 2009 sequel , he was convinced he was given a swirly by some jocks. After he and Alvin saw them picking on Theodore, he and Alvin attacked the bullies. Later, he is tricked into thinking that he is the school's litter monitor, only to find it was a joke. Simon has a crush on Jeanette. He cares deeply for Theodore and Alvin and their well-being, but wishes Alvin would act more mature and stand to learn more. He relishes Theodore's good nature but Alvin always takes to taking advantage of how gullible Theodore is, along with the fact that he is young and naive. He cares for Alvin even though they always fight, but he worries if somewhere deep down, they are alike.
In Alvin and the Chipmunks: Chipwrecked, Simon has an alternate personality caused by a spider bite. His alternate identity goes by the name Simone and speaks with a French accent. Simone is depicted to be braver than Simon and also is less uptight than Simon. Near the end of the movie Simon recovers from the bite and reverts back to his usual personality.
Simon is once again the brains of the Seville family. He frequently corrects Alvin (such as in Sister Act when Alvin misspells "in" as "inn") and uses his technical abilities to help improve his standard of living (rewiring a talking teddy bear in Talking Teddy or building a robot bodyguard in Bully For You). He retains his dry sense of humor and sardonic quips while frequently uttering stuttering responds (Clowning Around) or covering his ears (A Is For Alien) when he disagrees with something Alvin plans to do or say. Simon isn't afraid to stand up for what is right (Simon For President), though he slips on his duty sometimes such as in To Serve And Protect but ultimately takes the responsible action nevertheless.
Simon is commonly seen wearing a dark blue top and a pair of glasses. He is the tallest chipmunk, even slightly taller than Jeanette.
Before The Alvin Show Simon wore a red vest with an S on it. After The Alvin Show was created, Simon was given more human features, and instead of a red vest Simon began wearing a blue sweater, black glasses with light gray lenses, and black shoes.
In Chipmunk Punk, Simon's hair is spiky as if he were a rock star. He once again wears his black glasses, blue sweater, and all black shoes to match the style of the album.
In the Alvin and the Chipmunks series, Simon wears black glasses with white lenses, a blue sweater, and a pair of white and red patterned shoes. As the series progresses Simon's sweater becomes darker and his glasses become blue. By The Chipmunks Go to the Movies, his glasses are purple, although he had gold glasses in Batmunk.
Simon in the CGI films only wears a blue hoodie and a pair of black glasses that came from a toy Santa Claus. His appearance was modified to look more closely to a real life chipmunk.
His eyesight may not be as bad as Jeanette's because he still looks directly at the person he is speaking to and rarely bumps into things with his glasses off, both of which Jeanette does.
In ALVINNN!!! and The Chipmunks, Simon wears a two-different-shades-of-blue non-hooded sweater, dark blue jeans, white shoes with two grey stripes and large, blue-rimmed glasses.
Simon and Dave have a close relationship, because Dave takes care of the Chipmunks and Chipettes like they are his kids. Simon loves Dave and Dave loves Simon.
Simon and Alvin always seem to be fighting. Alvin always does something to make Simon mad. However, Simon is protective of Alvin and loves him.
Simon and Theodore also have a really close relationship. Simon always seems to be with Theodore most of the time, Simon is also often seen to be protective of Theodore. However, despite his protection of Theodore he values him just as much as his brother Alvin and foster parent Dave.
It is really obvious that Simon likes Jeanette. Jeanette likes Simon back. He shows his true affection for her through Simone and when they are on their raft, waiting for a rescue helicopter. My Sister The Weirdo shows that he can be jealous of others helping her instead of first asking him.
Simon and Brittany never show a romantic relationship. Simon often looks after Brittany, valuing her as a friend and not a romantic interest.
Simon and Eleanor don't like each other in a romantic way, but they are friends and they care about each other. Simon looks after Eleanor, just as he looks after Brittany, Alvin, Theodore and Jeanette.
Simon and Ryan are not friends. Even though Ryan is friends with Alvin, he still bullies Simon and Theodore. Simon is rather strict with Ryan.
|Simon: Since he feels it's as close to a world trip as he'll ever get. - (The Chipmunk Adventure)|
|Simon: Well, if you insist on going, don't take the easterly route. I heard on the news there's a hurricane coming in that direction! - (The Chipmunk Adventure)|
|Simon: We've got to keep these two apart. - (The Chipmunk Adventure)|
|Simon: Don't tell me what I want Arthur! You're the only man I've ever loved... will ever love! - (Meet Frankenstein)|
|Simon: That little glass of yours is always half full, isn't it? - (Meet Frankenstein)|
|Simon: Given the choice...I'm in. - (Meet the Wolfman)|
|Simon: Well, our lips are moving and words are coming out. - (Alvin and the Chipmunks)|
|Simon: They just did take us alive, Alvin. - (Alvin and the Chipmunks)|
|Simon: Glasses! Glasses! You wouldn't hit a guy with glasses, would you?! - (The Squeakquel)|
|Simon: Her glasses were quite fetching. - (The Squeakquel)|
|Simon: This is not just a spider! That's a phoneutria bahiensis; its bite contains a neurotoxin! - (Chipwrecked)|
|Simon: Jeanette and I are dating?! - (Chipwrecked)|
|Simon: Spare me the boo-hoo eyes, Alvin. - (Family Spirit)|
- The origin of his name comes from Simon Waronker.
- Simon is frequently regarded as the oldest of The Chipmunks given his height and maturity. In the 80s series, however, Alvin is actually older than him. It's not until the release of the Alvin and the Chipmunks: The Junior Novel does Simon become the oldest sibling. He retains this role into the new series, ALVINNN!!! and The Chipmunks.
- Throughout the franchise, Simon has constantly switched between wearing black glasses and blue glasses.