Kevin 11,000 is an alternate, more evil, version of Kevin Levin, which serves as the main antagonist in TV show; Ben 10 in the non-canon episode Ken 10.
In the distant future, (and presumably in an alternate timeline), Kevin has been trapped in the Null Void for about 32 years. While he was there, Kevin had been absorbing around 10,988 other aliens to acquire their powers. During one of his breakouts Kevin had a relationship with nameless woman and had a son named Devlin. He tricked his own son into believing that he's reformed and that he want to "Spend some quality time with his son," and that all he had to do was to is to find and open the Null Void Projector.
After Devlin tricked Ken Tennyson into showing him where the Null Void Projector was, Devlin opened the projector, releasing Kevin. When Ben found out, Kevin showed his true form. Kevin proved to be more than a match for both Ben, and Ken. When Devlin found out that he was tricked by his own father, Devlin decided to team up with the Tennyson and fight his father. When Ben witness Kevin beating up Ken and knocking him unconscious, he transforms into Way Big and beats up Kevin to, presumably, near death. When Ben and Ken walked away, Kevin got back up, proclaiming that, that was nothing. Eventually Ken manage to toss a Null Void Bomb right underneath Kevin, trapping Kevin inside the bomb, and presumably sending him back to the Null Void.
In this version, Kevin is more insane than ever and more powerful than ever. His determination to be better than Ben Tennyson has made him more crazy. He goes so far as to trick his own son so he can prove he's the best.
Like his original counterpart, Kevin 11,000's main ability is absorption. When he make physical contact with any alien, he can absorb their DNA, so he can gain their powers. He can also absorb the lifeforce of aliens so that he can mutate himself to become a hybrid of virtually every alien he's absorbed. According to pop-up facts of the episode, he has killed and absorbed the lifeforce of exactly 11,000 aliens.