Ben 10: Alien ForceCarl from the Alien Force/Ultimate Alien timeline first appears 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 Humungosaur 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 super 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.
Ben 10: Ultimate Alien
Carl reappeared in Hit 'Em Where They Live. He was ambushed by Charmcaster, Zombozo and Vulkanus. One of the trio 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.
- Like Frank, Carl knows about his father's secret and his mother's identity as an Anodite.
- Carl has a Plumber bazooka hidden in his attic, his current residence also being his childhood home.
- Unlike Sandra, Carl is softer on Ben, up to the point of letting him live his life. Carl seems to contradict Sandra when it comes to disciplining Ben, being more loose than stern, though like Sandra and one of his alternate counterparts, he insisted to be called by his name and yet Ben refers him as Dad.
- In the original series, Carl looks like a younger, thinner version of his father Max Tennyson, but with the same green eyes as his son, Ben, his niece, Gwen, and his nephew, Ken, and was voiced by Dee Bradley Baker (this Carl is from an alternate timeline), while in his only appearance in the Alien Force series, Carl's appearance was modeled after his live-action film actor, Doc McManus, from the live-action film, Ben 10: Race Against Time, who also provided Carl's voice.
- Given the similarity of their personalities, it is likely that Carl takes after his mother Verdona, although they have yet to be seen together on screen.
- In the novels, Carl's name is misspelled Karl.