Maxwell Tennyson is the elderly grandfather of Ben and Gwen Tennyson. He organised a Summer long road trip for both his grandkids to explore the various states of America. But on their first night, Ben found the Omnitrix and became a hero in the process. This forced Max to come clean with the kids and reveal that he was a Plumber, an agent of an Intergalactic Police Force that protects the galaxy. With his knowledge and experience in alien technology, he supports his grandkids to become heroes and protects the Earth along side them.

He was a plumber for about 30 years. Building a reputation that grants him as the most well-respected plumber in the galaxy, despite being one of the only humans to be one. 

He met another human plumber, Verdona, and they instantly fell in love. Fighting alongside through out the galaxy. They got married and had kids, but they both promised the plumber community to not let them know, especially their grandkids Ben and Gwen.

Max lost his arm from an epic battle with Vilgax, who also resulted in the death of Verdona.

His robotic arm is of alien origin, able to grant him enhanced strength and a variety of weapons for multiple uses. It’s even a communicator and extranet accessor.

Max has never heard of the Omnitrix. The Galvan are extremely secretive about their technology and only share it with those they deem worthy. Hence why Azmuth sent the Omnitrix to Earth for him in the first place.

Ben and Gwen didn’t find out his plumber history until pretty much instantly after Ben found the Omnitrix.

After they found out, Ben was more than ecstatic to learn that his grandpa was some intergalactic space cop. Gwen was more shocked and had some resentment to Max due to his years of lying. But she eventually came around and is proud that he’s her grandfather.

He lives in his motorhome “The Rustbucket”, and he often takes Ben and Gwen on road trips.

Max has extensive knowledge on alien biology and technology. He helped Ben understand each of his alien forms to the best of his knowledge, how to use his powers, and how to become a true hero.

Once Ben defeated Vilgax for the first time, Max was reinstated into the plumber ranks as a deputised Magister. Regularly attending meetings to the nearest plumber HQ and oversees his planet as his district.

An easy-going, kind, and normally jovial man, Max Tennyson often comes across as pleasantly absent-minded at times, but is actually quite perceptive. Max is a very brave man, having dedicated his life to preserve peace on Earth between humans and extraterrestrial life.