Kenneth Tennyson

''This article is about the cousin of Ben Tennyson and Gwen Tennyson's older brother. For the son of Ben 10,000, see here.''

Kenneth "Ken" Tennyson is the older cousin of Ben Tennyson, Gwen Tennyson'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. In his first, (and so-far only,) appearance, Ken Tennyson, the oldest grandchild of Max Tennyson, was abducted by DNAliens after they sabotaged his ride, the "Awesomobile," in order to flush Max Tennyson out of hiding as he was slowing down their operations on Earth.

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 new 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 aided 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 grandpa's apparent death.

Trivia

 * He is mentioned only in Max Out and Inside Man, making it seem as if Ken was made solely for this episode as a reason for Max to have been there.
 * It is also never revealed why Ken didn't go on the summer trip with his sister.
 * 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 Kevin, the Awesomobile "makes the Rustbucket look like a Ferrari".
 * According to Gwen, Ken took Ben to his first soccer practice and that he plays in a band, playing the bass guitar.