"Grandpa" Maxwell "Max" Tennyson is the highest-ranking Magister of the Plumbers (noted as the leader of the Plumbers on some occasions), as well as the grandfather to the legendary Ben Tennyson as well as cousin Gwen Tennyson.
- Max first appears in Clancy Strikes Back! where he is duped Clancy into being trapped underground without his technology.
- In New Girl, Max agrees to join the 10 Squad upon Ben's creation of the team.
Ben 10: Alien Universe
Back in Action: Alien Universe
- New Girl (first re-appearance)
- The Alternative (62 year old)
- Ben 10: Alien Universe Unleashed (killed; reborn)
- Hooking Up With the K's
- For whatever reason, Max's present self wasn't present when Paradox was showing the members of the 10 Squad footage of past Ben.
- He has been romantically involved with Verdona Tennyson, an Anodite with whom he conceived his two sons and that he met while on patrol who finds Max to have a "spark all his own" (referring to what she calls "The Spark" she normally finds in Anodites such as Gwen).
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