Carl is, along with Sheen, 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. An introverted weirdo of a nerd who is babied by his parents constantly, he is extremely proud of his weirdness and makes no attempt to hide his ecstatic personality.
Carl was always my favorite character in the show. Not Jimmy (I thought he was kinda annoying at times) and Sheen (he felt way too much like me and I couldn't handle that fact). Rob Paulsen's voice work as Carl is probably one of the best examples at how talented and versatile he is, going from playing snarkycomicreliefs, to an equally energetic yet different type of character.. you gotta admire the man.
For most of the character's appearances, he was played by Rob, but in one game the character was filled in by Wally Wingert. I remember playing this game as a kid and found Carl to be weird sounding.. I guess this is why. Wally does an admiral effort to match Rob's voice, but it just ends up sounding whiny as the impression goes a bit too far.