Lastly their's Ben and Gwen's Grandpa Max, who takes them on a cross country road trip in his RV The Rust Bucket. However Max knows more about the aliens and the Omnitrix then he's letting on. 

Details about Grandpa Max

- Max is still a retired plumber

- Max's left arm is actually mechanical but is cloaked to look like real arm

- Max looses his arm in his last battle with Vilgax

- Gets assistance from for tech from Phil another secret Plumber