Kevin Levin is a recurring former antagonist in Ben 10 and one of the main protagonists in Ben 10: Alien Force. His ability is to absorb every energy in the world. Ben met him one night in New York where they became best friends until Ben realized that he was a bad guy and Kevin absorbed enough of the energy from The Omnitrix so he could become any of the aliens inside and then mutates with all of them into a creature called Kevin 11. He later on is trapped in the Null Void for acoouple of years but luckilly escapes and then becomes best friends with Ben and Gwen's boyfriend.
Kevin Eleven Thousand is an alternate future version of Kevin Levin. His first appearance as the main antagonist of Ken 10 where he escapes the Null void by his son Devlin Levin. He mutates with tons of aliens in the Null void he encountere. He later on becomes an ally and best friend of Ben 10,000 where he helps defeat Vilgax for good.