Carl likes to eat, and this caused him to be overweight. 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 as he is shown to be the first 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.