Cooper Daniels is the grandson of one of Max's Plumber friends. He is half-human/half-Technomage.
Ben 10
Cooper in the Original series
He first appeared in Ben 10 vs. the Negative 10, where he was being given a ride home by Ben, Gwen and Max. It's later revealed that Cooper is a genius with technology, in part thanks to his unique technopathic-kinetic powers which allows him to communicate with and manipulate any sort of machinery. Such a power becomes crucial in defending the Mt. Rushmore base from the Negative 10.
Alien Force
Cooper reappears in Ben 10: Alien Force, where he's gained a considerable amount of weight due to spending too much time in his lab on the computer. The DNAliens capture him in Undercover and force him to build a mysterious arch and a holographic projector to hide it. He's released by Ben, Gwen and Kevin, and destroyed the projector. Cooper has since developed a crush on Gwen, which she can't help but be annoyed about. Although Kevin usually shows jealousy when other boys crush on Gwen, he's surprisingly good-humored towards Cooper's adolescent feelings.
Cooper later returns in War of the Worlds: Part 1 where he uses a robot suit he built out of objects in his lab to help fight the DNAliens. After studying the Omnitrix's ability to restore the DNAliens to humans, he dismantles his suit to create rayguns that copy the effect. In the end, he becomes a pupil under Max Tennyson.
Vilgax Attacks
He appears on Morotesi at a Plumber research station. He was tricked by Albedo (who was working for Vilgax) into doing research that helps Vilgax's plan. Upon discovering this Cooper helps Ben, Gwen, & Kevin on fight Vilgax's army & Albedo on MorOtesi.