|Relatives||Sandra Tennyson (wife)|
Carl first appeared in Grounded, where he and Sandra discover Ben's superhero activities. Apparently unable to handle the thought of their son constantly risking his life, and angered about Ben's constant lying about his activities, they ground him, forbid him from using the Omnitrix, and tell Gwen's parents of her superheroism, resulting in her grounding as well and Kevin being forced to fight the Highbreed alone.
Additionally, Carl was furious when he found out his father had something to do with it. When this proves to be too much for Kevin to handle, Ben openly defies his parents and uses the Omnitrix to turn into Humungousaur and, (literally) break out of the house and help Kevin; through this, they realize how important the things Ben is doing really is.
They come to help Ben and Kevin fight, and admitted that they are proud of Ben, allowing him to resume his heroism. During this time, Carl admits that he had known all along about Max's time in the Plumbers and resented him for it, but now realizes that he was protecting them, just as Ben was.
Carl reappeared in Hit 'Em Where They Live. He was ambushed by Charmcaster, Zombozo and Vulkanus. They flattened his car tire, making him unable to escape. They were about to strike when Ben, Gwen and Kevin came along and saved him. He was completely oblivious to what was happening.