He is a local genius and geek, who is very intelligent, but somewhat eccentric and timid. He was introduced after the show's retooling following the end of the first season, and seems to be Johnny's only friend, although Johnny often denies that.
Carl sometimes uses Johnny for his experiments' sake. Carl really likes Johnny and he continues to hang out with him, even after all of the mean things that Johnny does to Carl and says about him.
Carl remained in the show after the return to the original style, but was relegated to smaller roles. He is possibly descendant of Carlot, an alien with the self-proclaimed title of Destroyer of Worlds.
Carl sometimes visit johnny and go on adventures with the cyberchase fighters.