Carlton "Carl" Ulysses Wheezer is a major character in the franchise.
"Carl is Jimmy's best friend, but they couldn't be less alike. Carl is cautious and, well, kinda chicken, and he's prone to wheezing and carsickness. He demonstrates his asthma inhaler for show and tell, and at the amusement park, Carl spends his day trying to beat the guy who guesses allergies. But through it all, Carl is Jimmy's loyal buddy and biggest fan...and crash-test dummy for Jimmy's arsenal of inventions."
Carl has peach skin with freckles. He is characterized by his large, almost pear-shaped head with small black eyes that are fairly close together. He has short, thick orange hair which forms clump like structures of varying sizes at the top of his head, as well with the eyebrows of the same color/texture.
His body and face show that he is overweight, as they are round and don't reveal much about skeletal structure, though his arms and legs don't seem to have stored so much fat. He wears large brown circular glasses and has a short round, yet broad nose. He wears a light orange and coral short-sleeved vertically striped shirt, under a pair of orange suspenders, which connect to his dark green trousers. He also wears a pair of what appears to be light brown loafers.
Carl is quite gluttonous, loving to devour not only food but objects such as toys and newspapers. When his parents expanded their cable line-up, Carl found himself focusing on a channel devoted to llamas and a show about a superhero called Llama Boy the Super Hero. He has adored llamas ever since, going so far as to join a fan club, the Llama Love Society (which he likely created, since he is shown to be the only member). He even turned into a llama once. He is allergic to almost everything, and has asthma. Carl often unknowingly gives Jimmy his brilliant ideas.
It is revealed in "The Incredible Shrinking Town" that he took ventriloquist lessons, and that he can virtually imitate and sound just like everyone. It is also a hinted that he has some sort of dislike for Sheen, even though he's one of his best friends. Carl enjoys playing a video game called Llamapalooza. It is also revealed in I Dream of Jimmy and Carl Wheezer, Boy Genius that he is actually self-conscious about his unintelligence, and envious of Jimmy and wants to steal his life. Carl seems to specifically envy Jimmy's IQ and all the attention he gets from girls and is always upset that Jimmy makes him test his inventions, since he is sometimes harmed.
- In I Dream of Jimmy, he secretly dreams of Jimmy being his servant and tortures and mocks him in front of their class. In his dream, he is a genius and Jimmy is unintelligent, so Carl makes him look like a fool in front of the class and forces him to test inventions.
- In Stranded, he secretly hoards food while his friends are starving. Libby and Sheen become angry with him and try to throw him overboard, after they see if he has more food on him.
- Carl became the main antagonist in Carl Wheezer, Boy Genius. He betrays Jimmy for a chance with a girl he's never met, and starts verbally abusing him, even after the many times Jimmy saves his life. When Jimmy saves Carl for the third time, Carl blames Jimmy for everything (even though he was highly responsible) and pins all his insecurities on Jimmy.
- Sometimes, Carl stalks Judy to the point where he apparently wants to do away with Hugh.
- In Win Lose and Kaboom! we learn that Carl goes to Bolbi's house for cookies.
- Carl 'hosted' Rob Paulsen's "Talkin' Toons Podcast" on July 6th, 2012. In it, he reveals many hidden details including the fact that Doppy was just him in a costume, Sheen is currently in juvie (back on Earth after returning from Zeenu), and at one point he had a crush on Cindy. This most likely might be non-canon, since none of it has been confirmed in animation or any other form of media.
- It was revealed in The Incredible Shrinking Town, that Carl took ventriloquist lessons. He was going to sound like Cindy, but never got the chance. However, in the episode he did sound like Sasha and Zix.
- In Journey to the Center of Carl, It reveals that Carl eats his toys because it tastes fruity and chewy.
- When Carl's suspenders were removed in the TV series, the parts of where his suspenders pulled up his pants were still in the state of being pulled up when they were removed. This was fixed in Make Room for Daddy-O, but was still present in one scene with Carl in Love Potion 976/J and his cameo in Is This Cute?
- Carl has asthma and has a inhaler because of it, although the inhaler appeared less as the TV Series progressed.
Villains: King Goobot V | Professor Calamitous | Eustace Strych | Beautiful Gorgeous | Meldar Prime | Evil Jimmy | The Junkman | Zix, Travoltron and Tee | Baby Eddie | Gortox the Irritable | Dr. Sydney Moist