Paradox is an adult scientist that got sucked into a time machine and stays in nothing for 100,000 years, when he escapes. He can teleport and time travel. He teams up with Ben, Gwen, and Kevin Levin to battle the Trans-Dimensional Monster in the episode "Paradox". He gives Kevin a new car and turns him back into a teenager when he's a geezer. Sometime in the future Paradox teams up with Ben 10,000 at some point. Paradox has a watch that lets him keep track of time.

Paradox's First Appearance
Paradox (Episode)

Paradox's Last Appearance
War of the Worlds Part 2