|This article belongs to the Original Continuity.|
Not many details are provided on Max's childhood and background. In Permanent Retirement, Max's older sister, Vera Tennyson is introduced; she is seen as having her own weird taste in food, and is hinted as having knowledge that aliens are real. In Big Fat Alien Wedding, Max's older brother, Gordon Tennyson is introduced; in the events of the episode Gordon is also a Plumber, still on active duty, as is his wife, Betty Jean Tennyson, and their son, Joel Tennyson.
Max spent his childhood summers on his Uncle Jedediah's farm, where he learned about the merits of hard work.
Max, under the effects of Zombozo's happiness-draining, mentions having been afraid of heights as a kid and to beat his fear he climbed up to the top of the water tower and "scared the fear" right out of him.
Max has a childhood friend called Donovan GrandSmith, who says that Max always worried and was never a risk-taker like him. 30 years earlier, Donovan and Max had both been broke when Donovan offered Max a business opportunity, which he turned down. Max later became a Plumber (most people thought Max was just a regular plumber), establishing that Max's career as a Plumber lasted for about 28 years before he retired (Max mentioned that after 28 years on the job, he'd never figured out who was behind the Bermuda Triangle).
Max was an astronaut and would have been the first man on the moon, but he left the program before the Apollo Moon mission. In his own words, Max said he just 'took his step for mankind in other ways'. It is later revealed that he did in fact go into space, just not with NASA.
It is unknown if Max's strange taste in food was acquired from his adventures to other planets during his career as a Plumber, or if its root can be found in his childhood.
Max met Verdona when she was held captive by a Synthroid (a species of robotic aliens) that wants to use her Anodite powers as fuel for their planet. Max saved Verdona and Magister Labrid, the latter of whom recruited him as a Plumber. 
Grandpa Max is a Plumber, who takes his grandchildren Ben and Gwen on a cross-country trip, during which Ben discovers an alien watch, the Omnitrix. His grandson uses the watch to become the superhero "Ben 10". Max helps his grandson fight bad guys and aliens, and he also teaches Ben to use the watch responsibly.
During their adventures, Gwen and Ben question Max's uncanny knowledge, and the fact he doesn't seem to be bothered by all the weirdness they encounter. It is eventually revealed that Max and the alien warlord Vilgax are old enemies.
Later, Max reveals he is part of an intergalactic police force known as the Plumbers, and that he fought and defeated Vilgax years before. During the episode he meets his old partner Phil Billings. He discovers 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.