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, he insisted to be called by his name.
Carl chronologically first appeared in Destroy All Aliens, where he and Sandra ground Ben for not telling them where he went as well as for the mysterious footprints that were on the floor and a mishap in Ben's school where the Omnitrix accidentally teleported his homework. They forced Ben to stay home and complete a history report. Later on, Carl and Sandra inform Max and Gwen that Ben has escaped the house and Grey Matter enters into their house where Carl and Sandra discover the creature. After Sandra begins attacking Grey Matter, he is thrown outside and transforms into Diamondhead. Sandra passes out and Max knocks Carl. Afterward, the Omnitrix malfunctions and transforms him into Wildmutt and transforms Sandra into Heatblast. Eventually, Gwen and Ben use the Omnitrix to transform him and Sandra back into normal and they, having forgotten that they grounded Ben, allow for Ben to go on a fishing trip with Grandpa Max and Gwen.
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 the mission 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.
- Ben 10: Destroy All Aliens (first chronological appearance)
Ben 10: Alien Force
- Grounded (first appearance)
Ben 10: Ultimate Alien
Cartoon Network Action Packs
- Double Trouble
- Lazy Day
- According to Derrick J. Wyatt, he and Sandra approve of Ben's friendship with Rook.
- 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.
- In the novels, Carl's name is misspelled Karl.