Kevin Levin

For a time, Kevin Levin was a villain in the cartoon series Ben 10. In the premiere of Ben 10: Alien Force, he became a hero and joined his former rival / new friend, Ben Tennyson to fight against extraterrestrial activities.

Then on Ben 10: Ultimate Alien episode, The Forge of Creation, he absorbs the Ultimatrix and becomes insane once again and a lot more dangerous than before.

Origin
When Ben found him, Kevin lived alone and stole from people in order to get by. Ben befriended him once he found out that Kevin, too, had special powers. Then, when Kevin tried to commit a crime out of spite, Ben tried to stop him and persuade him to use his powers for good. Kevin grew resentful of Ben and later returned as an enemy.

In the first episode of Ben 10: Alien Force, Kevin joins Ben and Gwen to battle against evil.

It is revealed in the episode of Ben 10: Ultimate Alien, Ultimate Aggregor, that when he absorbed raw energy, he became insane, which happens to the rest of the Osmosians. Later in the episode The Forge of Creation, he absorbs the Ultimatrix in order to stop Aggregor from absorbing a baby Alien X, but it does more harm than good after he goes insane again. After Aggregor has been defeated, he flies off, leaving both 10 and 16 year old Ben and 16 year old Gwen behind. In the next episode, ...Nor Iron Bars A Cage, It's reveiled how Kevin escaped from the Null Void and how he turned back to normal between the original series and Alien Force and how he had gotten his material absorbing powers. In the same episode, he volentarlly goes back to the Null Void to get revenge on his prison's warden, Morgg. He almost got his vendetta on Morgg, and leaves the prison, thinking that he did kill him. Gwen still thinks that Kevin could get his sence back and go back to normal, but Ben says that they now might have to "put him down", meaning that Kevin might have to be killed. However, as of the end of the season one finale episode, "Absolute Power: Part Two", Ben and the others restored Kevin back to normal, and Kevin is once again a good guy.

Powers and Abilities
Kevin has the ability to absorb any solid matter he touches like stone, metal, and crystal, and have it cover his entire body. He is also able to shapeshift his arms when coated in solid matter and repair cracks with a simple touch.