KEVIN 11 (Ben 10D)

Kevin Ethan Levin, better known as KEVIN 11, is the arch-rival turned best-friend of Ben Tennyson.

Once a petty delinquent, then a sociopathic super-villain, then an anti-hero and uneasy ally, Kevin eventually became a great hero himself, and an honorary member of Team Tennyson. With the ability to mutate himself into more powerful forms, thanks to his Osmosian DNA, he's second only to Ben Tennyson as the most powerful being in the Universe.