Maxwell "Max" Tennyson, or Grandpa Max as his grandchildren call him, is the paternal grandfather of cousins Ben Tennyson and Gwen Tennyson. He is in his 60's, rather overweight and a bit slow at times, but with a keen sense for adventure and a strange taste in food -- the only topic on which Ben and Gwen never argue. Max ends up taking the kids on an interesting Summer Vacation Roadtrip across the United States and back.
Grandpa Max is a Plumber, who takes his grandchildren Ben and Gwen on a cross-country trip, during which Ben discovers an alien watch, the Omnitrix. His grandson uses the watch to become the superhero Ben 10. Max helps his grandchild fight bad guys and aliens, he also teaches Ben to use the watch responsibly. During their adventures, Gwen and Ben question Max's uncanny knowledge and the fact he doesn't seem to be bothered by all the weirdness they encounter. It is eventually revealed that Max and the alien warlord Vilgax are old enemies.
Max is an overweight old man with fair skin, black eyes, and gray hair. He wears a white shirt underneath a red button-up Hawaiian shirt with a floral design, blue jeans, and brown shoes.
In the Heroes United Arc, Max retains his red Hawaiian shirt, but his undershirt is now black. He also wears white trousers and gray shoes with black soles.
In a few flashbacks of the Heroes United Arc, Max wears his red Hawaiian shirt and white undershirt with brown pants and a pair of black shoes.
6 Years Ago, Grandpa Max sends Eon to the Null Void with a Null-Void projector after Ben and Gwen defeated him. Before getting sent away, however, Eon states that he will return in 6 years. 6 Years Later, Grandpa Max was on a road-trip with Ben, Gwen, Kevin, and They were minding their own business, when suddenly, they ran into Eon, who had escaped from the Null Void. He tries to take the Omnitrix, but to no avail. But he manages to destroy the Null Void Projector before leaving. This forces Max to find some old fellow plumbers to help him take down Eon. During their trip, Kevin decides to take Gwen to a dog show for Valentine's Day, considering that she loves dogs. On the way, Max accidentally rear-ends someone else's car. The owner turns out to be Fredrick Jones, the host of the dog show with his dog Ellie(NOTE: The dog show part takes place around the same time as the Family Guy episode "Boy (Dog) Meets Girl (Dog)"). Once Frederick recognizes Ben Tennyson, he decides to let it slide. He also offers them free access to the dog show. While Max looks for one of the plumbers, Ben and his friends watch the dog show. After Brian won, they were shocked to learn that the breeding was public. Then, Eon returns and turns everyone he touched into Senior-Citizen-like Zombies. Ben, Gwen, and Kevin manage to rescue Stewie and Brian and meet Max at the Rust Bucket. They then learn that Carter is one of the 2 plumbers the team is searching for. They spend the night at his mansion before heading to Massachusetts to find the second plumber, who is Caillou's grandfather Hadley, who was visiting at the time. Hadley sends a note to Tom and Caillou, telling them to meet at his house. Once they arrive, they head to Bellwood and spend a week there. During the week, they go to the movies, Ikea, the Stadium Theatre, a variety of restaurants, and Froyo World, While Max stayed behind and worked with the plumbers. Eventually, Ben and his team head to Eon's hideout and successfully defeat him after a rough battle. Afterwards, they all part ways.
Max sends Ben, Gwen, Kevin, and Rook on a mission to track down an unknown alien species that he found to make sure it is harmless. Unfortunately, it was not harmless, as the alien has the ability to turn people into alien zombies just by biting them. Eventually, Grandpa Max got bit himself while trying to protect Ben from the aliens. He then passed out, and Ben took him to a meeting room for protection. Max told him to leave because he was gonna turn. He then told him to find Frederick Jones before turning into an alien zombie.
Nothing about "Road to the Omniverse" is real or canon, it's just fan-fiction. The Movie Road to the Omniverse" doesn't actually exist. All Ben 10 Characters belong to Cartoon Network.