Carl Tennyson

Carl Tennyson is Max Tennyson's son, Sandra's husband and Ben's father.

Race Against Time
In the live-action film Ben 10: Race Against Time, he is depicted as a new-age style parent who wants Ben to have his "freedom," insisting on being called "Carl", not "daddy", "dad" or "father", and letting Ben run off on mysterious adventures without asking questions. Carl wants his wife to give their son some freedom. He seems to be even more laid back than his wife, and is seen at least twice telling her to let Ben have his fun. For instance, near the end when Ben's mother tells him to not eat too much cheese, Carl says to "Let the kid live a little. Eat all the cheese you want, Ben!"

Original series
In his first animated appearance, Goodbye and Good Riddance, he is shown to resent his father, as his work as a plumber(the sanitary kind) prevented him from spending time with his family. He finds out about the Plumbers and the Omnitrix the hard way when Vilgax destroys their house and holds him hostage, leading to Ben as Cannonbolt saving him. He later assists Ben, Gwen, and Max in defeating Vilgax, and inside a gutter, he turns gas pipeline on and sets fire to it while XLR8 saves him and Vilgax is caught in the explosion and is supposedly killed. He offers Max dinner but since Vilgax had destroyed their home he couldn't. Max tells him that he could cook something in the Rust Bucket. Knowing Max's weird taste for food, he says that it would be better to go to some restaurant.

Alien Force
Carl later appears in the Ben 10: Alien Force episode, Grounded, where he and Sandra discover that Ben has resumed his superhero activities alongside Gwen and Kevin(though it appears this was the first time they discovered this, thus making Goodbye and Good Riddance non-canon). 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 Humongosaur and(literally) break out of the house and help Kevin; through this, they realize just how important Ben is to the world. They later come to help Ben and Kevin fight(shooting a Highbreed Commander with Max's ray gun), and admit that they are proud of Ben, openly allowing him to resume his superheroism. In this episode, he is modeled after and voiced by the actor who played his live-action counterpart in the film. His face also looks longer in Alien Force.

Ultimate Alien
Carl reappeared in the episode 'Hit 'em where they live'. He was ambushed by Charmcaster, Zombozo and Vulkanus. One of the trio flattened his car tyre, enabling him to get away. They were about to strike when Ben, Gwen and Kevin came along and saved him. He was completely oblivious that any of it was happening, Even when there was confetti raining from the sky.

Trivia

 * Like his brother Frank, Carl he know's about his father's secret and his mother's identity as an Anodite.
 * He appeared to be in possesion of a plumber bazooka hidden in his attic, his current residence also being his childhood home.
 * In his only appearence 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 neice, Gwen, and his nephew, Ken, and was voiced by Dee Bradley Baker, while in his only appearance in the Alien Force series, Carl's appearence 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 as well.
 * Carl is probably half human half anodite, but just without the spark.