Billy is a supporting character of Martin Mystery.
He is voiced by Samuel Vincent.
He is a tiny green alien who works for "The Center", as M.O.M.'s personal secretary, often seen flying on his mini hovercraft.
He is a powerful idolizer of Martin and in one episode, it was revealed that he even has a picture of Martin (making him the "crazed fan of the show" archetype). Usually he is first seen greeting the gang, once they are signed in and often does his signature high five with Martin.
His role is generally a supportive one; he pops in sometimes during a mission to give Martin, Diana, and Java valuable information, usually startling them in the process. He also does analyses on slime or fabric samples sent by Martin during a mission. However, he won't help Martin and the gang on a mission directly unless he is forced to.
In the second season, Billy was revealed to have once been a great alien warrior, known as Ganthar, on another planet, but he gave up violence for good. When Martin asked why a planet on Billy's list of hologram worlds was blue, it was revealed by M.O.M. to be the world which changed Ganthar into Billy, which is the reason he doesn't go on missions with the other three agents. He arrived on Earth in the Roswell UFO Incident in 1947. Billy adopted a human disguise — the "B.S. 1000" — to be with Martin and Diana at their school. There are a few episodes in season 3, in which it is hinted that he liked Diana, such as one of the Christmas specials where he invited her under the mistletoe and actually went on a friendly date with her. It is revealed in the episode "Revenge of the Doppelganger" that Billy was once a supermodel on his home planet.
- He share voice actor with Martin Mystery.
- This might be true, since he was fearsome and powerful, he might have been popular with his people.