Ken Tennyson (also called "Kenny") is a college student and Gwen's older brother. In "Max Out", he is captured by the DNAliens and mutated into one of their own through an alien parasite. Enslaved to the alien's will, Ken captures Grandpa Max and later fights Ben and company. Gwen restrains him while Ben uses the Omnitrix to repair the damage caused by the parasite, separating it from Ken. Ken then assists in destroying the parasite eggs being shipped from the factory. He is admired by Ben and Gwen. Ken Tennyson is Max Tennyson's eldest grandson. His nephew Ken Tennyson was named after him. He is Ken Tennyson Sr. while his nephew is Ken Tennyson Jr.

Ken Tennyson has made one appearance in Ben 10: Alien Force.

Ken Tennyson (Gwen's Brother's) First Appearance
Max Out
Ken Tennyson (Gwen's Brother's) Last Appearance
Max Out