Billy

This Billy look-alike alien is revealed to be a Maxatomar in the Ben 10 week alien pop-up. He made his first appearance in Ben 10 episode "Ken 10" where he was one of the few children invited to Ken's tenth birthday party. Impressed with, as well as somewhat jealous of, Ken's father, this alien revealed that his father is a dentist.

Trivia

 * He is based off of Billy, one of the main characters in The Grim Adventures of Billy and Mandy. His species, the Maxatomar, is also named after Maxwell Atoms, the creator of the aforementioned show.
 * Richard Steven Horvitz voiced this character as well as Billy.
 * Another similatity is that this alien's father is a dentist, an occupation that Billy's dad holds.