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 Ken 10 where he was one of the few children invited to Kenny's tenth birthday party. Impressed with, as well as somewhat jealous of, Kenny's father, Billy Alien revealed that his father is a dentist.

In Omniverse He later returns in characters background.

Trivia

 * He is based on Billy, one of the main characters in the Cartoon Network original series, The Grim Adventures of Billy and Mandy. His species, the Maxatomar, is also named after Maxwell Atoms, the creator of the mentioned show.
 * Richard Steven Horvitz, the voice actor of this character, also voiced Billy.
 * Both episodes he's appeared in so far are connected to Toepick; Ken 10 is when the alien is mentioned for the first time and Special Delivery is when it appears for the first time.