The leader of the Butt-Uglies. He wears yellow.
- Glad I Thought of It: In the premiere episode "Playback/Payback" he takes credit for 2T Fru-T's idea of replacing the search bot's footage with footage of a staged invasion, remarking "Am I a genius or what?"
- The Leader: He's in charge of the team.
The brains of the Butt-Uglies. He wears blue.
- Blue Is Heroic: He's a heroic Martian clad in blue.
- The Smart Guy: He serves as the smartest of the three Martians.
The brawn of the Butt-Uglies. He wears red.
- Big Eater: He has a voracious appetite.
- Red Is Heroic: He wears a red uniform.
- Stout Strength: He has a gut, but that doesn't hinder him from being remarkably strong.
One of the three youngsters the Butt Uglies hang with.
- Goggles Do Nothing: He wears goggles above his eyes for no explicit reason.
The second of the three youngsters who have befriended the Butt Uglies.
- Only Sane Man: She tends to be more sensible than Mike, Cedric, and the Butt-Uglies.
- The Smurfette Principle: She's the only main character who is female.
The third of the Butt Uglies' human friends.
- Black and Nerdy: He's a black nerd.
- Innocent Prodigy: It's mentioned by his friends that he's skipped a couple of grades, but his maturity level is still that which is expected from people his age.
- Nerd Glasses: He wears glasses.
- The Smart Guy: The most intelligent of the Martians' human friends.
A self-proclaimed alien hunter who has often been at odds with the Butt-Uglies.
- Cool Car: His hover-van.
- Hero Antagonist: He frequently tries to hunt down the Butt-Uglies out of concern that they're out to harm humanity.
- Laser-Guided Amnesia: The Butt-Uglies frequently erase his memories whenever he discovers too much.
- Reasonable Authority Figure: He understands that not all extraterrestrials are evil and is willing to allow the Butt-Uglies' human friends to provide proof that the Martians are not evil.
A geek who works at the Quantum Burger.
- Burger Fool: He works at the Quantum Burger fast food restaurant.
- Hero-Worshipper: He idolizes Stoat Muldoon.
- Nerd Glasses: He's a bespectacled nerd.
- Recurring Extra: He usually has no major role other than to be a bystander or to give someone for Stoat to talk to other than the Butt-Uglies and their friends.
A female Martian who is on the Butt-Uglies' side, but pretends to be on board with invading Earth so that Emperor Bog's not any wiser.
- Bizarre Sexual Dimorphism: She is prettier and more humanoid than all the male Martians.
- Hello, Nurse!: All three of the Butt-Uglies are smitten by her.
- Pink Means Feminine: Her uniform and the top of her head are both pink.
- Repetitive Name: Her first and last name are exactly the same.
- Reverse Mole: She pretends to be on Bog's side to help prevent him from finding out the Butt-Uglies have chosen not to invade Earth.
The Martian Emperor, who is most unamused by the news that the Butt-Uglies haven't been conquering Earth.
- Big Bad: A fair portion of the show's conflict revolves around the Butt-Uglies preventing Emperor Bog from finding out that they've neglected their invasion duties and to prevent him from starting an invasion on his own terms once he discovers the truth.
- Evil Overlooker: He is shown looming over the Butt-Uglies near the end of the title sequence.
A Martian scientist serving as Bog's second-in-command.
- The Dragon: He's Bog's right-hand man.
- It Is Pronounced "Tro-PAY": His surname is pronounced "Duh-mahj".
- Lame Rhyme Dodge: A recurring gag has him insult Emperor Bog under his breath and cover it up by claiming to have said something that rhymes when Bog gets angry at him.
- Mad Scientist: He's a Martian scientist who loves creating dangerous devices.
- The Starscream: He secretly plans to overthrow Bog.
Doctor Brady Hacksaw
A human scientist obsessed with dissecting aliens. Unlike Muldoon, he's not open to the possibility of aliens being friendly.
- Bald of Evil: He is balding and a very unscrupulous and cruel scientist.
- Broken Pedestal: It is mentioned by Stoat Muldoon that he used to be Hacksaw's intern, but had a falling out with him due to being put off by his ruthless ways.
- Fantastic Racism: He only sees aliens as carcasses that need to be dissected for the sake of scientific discovery and doesn't care at all that they're sentient beings.
- Jerkass: As if his dehumanizing of aliens isn't bad enough, he's also generally dismissive and rude to everyone else.
- Mad Scientist: He's obsessed with dissecting aliens and has no regard for their life whatsoever.
- Names to Run Away from Really Fast: Would you trust a person whose surname was Hacksaw?