Max Tennyson (Classic)/Ben 10

Max was a retired Plumber, who took his grandchildren Ben and Gwen on a cross-country trip, during which Ben discovers an alien watch, the Omnitrix. 
During their adventures, Ben and Gwen questioned Max's uncanny knowledge, and the fact he didn't seem to be bothered by all the weirdness they encountered. It was eventually revealed in Secrets that Max and the alien warlord Vilgax were old enemies.
In Truth, Max revealed he was part of an intergalactic police force known as the Plumbers, and that he fought and defeated Vilgax years before. During the episode, he met his old partner Phil Billings. He discovered that Phil stole the Null Void Projector, using it to make easy money, by freeing the aliens who the Plumbers had already captured, then fighting and catching them for profit.
In the episode Perfect Day, Max was given superpowers by Ultra Ben in Ben's dream. As Ultra Grandpa he had enhanced strength and was able to fly.