Main characters

• Tommy Cadle (voiced by Charlie Schlatter) - He was once a normal kid who had no cares in the world and did well in school, at least until the aliens came along. Tommy is often bullied by some of the other kids because of the aliens' actions and is annoyed by them, but generally accepts them as part of his life and sees Dinko as his best friend. Dinko always refers to him as "Tommy of Earth".
• Dinko (voiced by Charlie Adler) - A Pterodactylus-like alien that is the leader and biggest troublemaker of the alien gang, and Tommy's best friend. He and Gumpers always try to help Tommy, but they always mucks things up, often because they misunderstand Tommy's words to the point of insanity. Often Dinko will go to extreme measures to solve his curiosity to these words and earth rituals. This all leads to Tommy getting punished and/or blamed for everything and the aliens get off scot-free.
• Gumpers (voiced by Jess Harnell) - A strong, but easily scared gorilla-like alien with a big appetite. He appears to be extremely dumb most of the time, but he is capable of intelligent thoughts if he strains his brain hard enough. He and Dinko try to help Tommy with his problems, but they always mess things up and cause a bigger issue. Sometimes, Gumpers will point out the flaws in Dinko's plans, but Dinko never listens to him and does what he wants instead.
• Swanky (voiced by Jess Harnell) - Swanky is a British-accented insect-like alien that is the most refined of the gang. He is rude, lazy, elegant and very self-centered. He rarely accompanies Tommy and the aliens on their wacky adventures. He enjoys fancy things and massages and wants to steal Tommy's room for himself.
• Flip (voiced by Charlie Adler) - An energetic parrot-like alien whose speech is often unintelligible.
• Scruffy Dinko's pet dog who jumps like a hare and whose tongue supposedly is smarter than himself.

Major characters

• Gabby (voiced by Candi Milo) - a girl who is in love with Tommy, but unfortunately he doesn't feel the same way. In several episodes it is revealed that she can smell when Tommy is in trouble.
• Granville DeSpray (voiced by Jess Harnell) - a direct descendant of DeSpray Bay's founders, and as such he values old English traditions like teatime. Oddly, all the characters think he is Norwegian. Granville is hopelessly in love with Melba and has numerous times, to no avail, attempted to win her heart. He hates Tommy and always blames him for anything bad that happens. He only has one friend; the statue Admiral Puff. He has another dog statue named Jean Claude. He always tries to impress Melba by acting street and displaying hip-and-hop.
• Clinton Fillmore Jefferson XIII (voiced by Charlie Schlatter) - Clinton competes in any kind of sports available and usually wins. He is also a bully who likes to annoy others including Tommy. He has a Canadian accent and his catchphrase is "Losah!" which he refers to people as.
• Melba Manners (voiced by Candi Milo) - A spoiled brat who is the arch-enemy of Tommy. She enjoys forcing him to do tedious or tiresome tasks and has a loud and shrill voice. She is also an exceptionally clever opponent in staring competitions. Like the other humans, she is too stupid to tell that the aliens are aliens. She just calls them Tommy's "things".
• Cap'n Spangley (voiced b Charlie Adler) - An old sailor who is a little crazy. He is afraid of water and crustaceans and he runs the local taffy shop which Tommy and the aliens visit often.

Minor/recurring characters

• Tommy's Mom (voiced by Candi Milo) - A woman who lives in a house located near to Tommy's lighthouse. The viewers never get to see her, as she keeps contact with her son solely through a speaker installed in Tommy's bedroom.
• Old Man Bitters - Cap'n Spangley's archenemy.
• Emperor Breet - An evil emperor who now and then journeys to Earth to kidnap the aliens living with Tommy. Unfortunately, he always loses the right to take them in a game he isn't very clever at, and therefore despises: musical chairs.
• Doctor Daffodil (voiced by Charlie Adler) - An octopus-like alien that Dinko and his friends consults whenever Tommy needs a doctor. Unfortunately, his methods can be highly dangerous and Tommy therefore tries to evade him as much as possible.
• Tommy's Teacher (voiced by Candi Milo) - She usually appears in some episodes that revolve in school. In one episode, she gave Tommy his first B− for his inflated hand and degraded it to a C+ when the hand shrunk and to a C− when his leg inflated.
• Mom-sicle and Popsicle - Swanky's parents who are red-necked unlike their son.
• The Mime - A mime that tries to enter the lighthouse but is always stopped by Flip.
• The Frog - A banjo-playing frog that appears in some episodes often as intermission for a new scene or a gag.

Season 1 (2005)

Season 2 (2005)