|Age||18 (Alien Force)|
|Relatives|| Frank Tennyson (father)|
Natalie Tennyson (mother)
Gwen Tennyson (sister)
Carl Tennyson (paternal uncle)
Sandra Tennyson (aunt-by-marriage)
Ben Tennyson (paternal cousin)
Max Tennyson (grandfather)
Gordon Tennyson (paternal grand uncle)
Betty Jean Tennyson (grand aunt-by-marriage)
Joel Tennyson (first cousin once removed)
Vera Tennyson (grand aunt)
|Voice Actor||Will Friedle|
|First Appearance||Max Out|
Kenneth "Ken" Tennyson is the older cousin of Ben, Gwen's older brother, and son of Frank and Natalie Tennyson that they both looked up to. Ken Tennyson was never mentioned or even alluded to during the run of the original series.
Ken's failure to regularly contact his parents led to his disappearance coming to the attention of his younger sister, Gwen, and cousin, Ben Tennyson. After being traced to his last known location, Ken's trail was first followed by his Grandpa Max, who tracked him down to an DNAlien Hatchery. Ken, having previously known nothing about his grandfather's former life as a Plumber, was questioned by a DNAlien for any information, but Ken knowing nothing, the DNAlien, having already known that Ken knew nothing, placed a Xenocyte on Ken's face, which began to convert him into a DNAlien.
When Max infiltrates the Hatchery to free Ken, Ken was already partially converted into a DNAlien and attacked his own grandfather for the Highbreed. When Ben, Gwen, and Kevin infiltrated the Hatchery having followed Max's trail, they're ambushed by a swarm of DNAliens, Ken among them. When Gwen sees her brother almost completely changed into a DNAlien, she restrains him and prevents him from being attacked by Ben and Kevin--they having not recognized him yet.
At Ben's confirmation, Ben and the Omnitrix together restored Ken to his human form. Along side the others, Ken aids them in rescuing Max, who reveals that he'd been keeping up-to-date with all of their experiences since his disappearance. While Max goes to shut down the Hatchery, Ken helps the others destroy the DNAliens shipment of Xenocyte eggs.
When Max Tennyson seemingly sacrificed himself to bring down the Highbreed in charge of the operation with a makeshift Null Void grenade, Ken Tennyson was present at his grandfather's apparent death.
Ben 10: Alien Force
- Max Out (first appearance)
- As noted by Kevin, Ken continues the running gag where his name, Ben's and Gwen's all rhyme with each other.
- Ken, like Ben and Gwen, has green-colored eyes.
- Ken drives an old Junker car which, according to Ben and Gwen, Ken calls the "Awesomobile."
- According to Gwen, Ken took Ben to his first soccer practice and that he plays the bass guitar in a band.