Maxwell Tennyson
From Wikitrix
Maxwell "Max" Tennyson, or Grandpa Max as his grandchildren call him, is the 60-year old paternal grandfather of cousins Ben and Gwen Tennyson. With a keen sense for adventure and a strange taste in food (the only topic on which Ben and Gwen are always of a common mind), Max always ends up taking the kids on interesting trips. As soon as school lets out, Ben looks forward to going on a traditional summer road trip with Max. Much to Ben's annoyance, Ben discovers that his cousin Gwen (whom he dislikes) is joining them as well. Max travels in a motorhome nicknamed "The Rust Bucket", which he has modified with advanced technology. The Rust Bucket is a replica of a GMC Classic Motorhome.
Max Tennyson is Kenneth Tennyson's Great Grandpa.
Max was once in the army, had joined the astronaut program, and was a "plumber" (among other things, it seems) and has been through his share of scrapes, takes his grandson gaining superpowers in stride, and supports Ben in any way he can. Ben and Gwen were ignorant of this at first, believing him to have been a literal plumber. They began questioning this after several incidents in which he displayed knowledge and skills that a plumber would not normally have; everything from military-style hand signals to a working knowledge of nuclear reactors. Max and Vilgax are also old enemies, with Vilgax even going so far as to call Max "a thorn in [his] side."
In reality, Max was indeed a plumber, but not the kind that Ben and Gwen thought he was. He was part of a government organization called "The Plumbers" which dealt with extra-terrestrial, paranormal, and other situations that many others could not handle. Their base was beneath Mount Rushmore. The group was disbanded shortly after Max defeated Vilgax for the first time, suggesting that Vilgax had been largely responsible for the various incidents they dealt with. Max was to have been among the candidates eligible for the Apollo 11 mission, and would have gone were it not for other concerns.
By the age of 80, Max has further modified his RV, grown a beard, and seems to have lost his arm. In its place, he uses a neuroprosthetic replica of his arm, which can also extend and transform into a laser. He still retains his caring personality.
Max is an old friend of an alien named Xylene. She had intended to send the Omnitrix to Max, but Ben found it by accident. Max and Xylene seem to have been romantically involved and work well as a team. Xylene tries to convince Max to form a partnership and travel across the galaxy with her, but Max eventually turns her down twice: the first time due to his duties as a Plumber, and the second time due to his need to look after the kids.
see also: Benjamin Tennyson, Gwendolyn Tennyson, The Plumbers, Xylene, Tennyson Family