2-T-Fru-T - 2-T-Fru-T is the mechanic (described on the BUM merchadise as a "tech officer", he is most likely a lieutenant as he is of lower status than B-Bop but higher than Do-Wah) for the Butt-Uglies and inventor of BKM. Sometimes B.Bop and Do-Wah can pick on 2-T although they are his friends. A mechanical prodigy, 2-T is the MacGyver of Martians and has been able to construct anything from invisibility rays to the BKM (Butt Kicking Mode) suits using parts that were immediately available. He often finds himself at the mercy of sub-standard parts sent to him by Dr. Damage, ironically, but these never slow him down for long. 2-T is a bit socially inept, often forgetting Earth colloquialisms and fading into technical jargon when it's not necessary. He's also a bad liar under stress, although he can think of a good cover story whenever B-Bop is indesposed. He's usually calm, but has been known to snap at his friends whenever he feels betrayed (this may be insecurity; one episode has him stopping Muldoon in his usual slew of anti-alien insults with a cracking voice, as if he's about to cry). He wears a blue uniform and BKM suit. Tech officer 2-T-Fru-T was voiced by Rob Paulsen.
Do-Wah-Diddy - Do-Wah-Diddy is the fun Martian of the Butt-Uglies. Do-Wah has a huge appetite and loves milkshakes, hamburgers, junk food and all other unhealthy foods. Not surprisingly, Do-Wah is the fattest of the Martians (although not obese). Despite a prominent belly, Do-Wah has super-Martian strength (Martians on the show are stronger than humans by themselves, so this is a particularly powerful statement). Despite his thickness (or possibly because of it), he is extraordinarily sweet and usually the first to look on the bright side and find the good in people. Do-Wah has a light crush on Angela, the show's only female human. Do-Wah-Diddy wears a red uniform and BKM suit, and the merchandise gave his rank as a corporal. Corporal Do-Wah-Diddy was voiced by Jess Harnell.
Shaboom Shaboom - A female Martian secret agent. She's aware of the trio's defection but keeps it a secret, and it's often implied that the Butt-Uglies have crushes on her. Shaboom Shaboom was voiced by Kath Soucie.
Mike Ellis - A red-headed, green eyed 13-year-old boy, Mike is the unofficial and sometimes debatable leader of the human friends of the Martians. A typical teenager, Mike enjoys TV, junk food, hoverboarding, and the newest pop music. Mike is prone to bouts of big headedness, much like B-Bop, but can also get his confidence shattered readily whenever he's upset. Mike's also a pessimist at times, but is the first to jump in and take charge whenver the situation calls for it. Along the course of the show, Mike has been exposed to deadly radiation, electrocuted, kidnapped (twice), and subjected to several other unearthly threats. Mike hates it when people call him "Mikey".
Angela Young - The only female human ever shown on the show, Angela is a dark haired, blue-eyed teenage girl. Angela is level-headed and smart, often the voice of reason to the more reckless male characters on the show. Much to Mike's dismay, she is also very good at video games (breaking another stereotype in the process) and once saved the world with her skills with a joystick. Angela is typically considered beautiful by other alien species, and has been kidnapped twice as a result. Both instances had her fighting her kidnapper, but being rescued by the Martians anyway. Not quite a tomboy, Angela will sometimes "squeak" when she talks, especially when she's excited. Angela acknowledges that Do-Wah has a crush on her; whether she likes him back romantically is debatable.
Cedric - A 12-year-old African American, Cedric hangs out with Mike and Angela (he was moved forward in school, which explains his age and his height). Cedric has big glasses and, for some reason, brown eyes that reflect silver if the light hits them the right way (this was most likely an animation glitch or the light reflecting off of his glasses, as it is never addressed on the show). He is a technical wizard akin to 2-T, although he is more of a computer hacker than a mechanic. Cedric also has incredible aim, able to hit very small targets from very far away. Cedric tends to make corny jokes which either go unheard or make him the target of strange looks. Cedric can be very nervous, and is sometimes seen wringing his hands in worry. Surprisingly, Cedric is obsessed with fame and, more importantly, fortune, with his quest for money leading to almost callousness towards his friends (although, in the end, he always pulls through). Overall, he's a good person. Cedric was never given a last name on the show.
Stoat Muldoon - Stoat Muldoon is an overly zealous alien hunter who discovers the martians on Earth several times throughout the series, but every time he has, the Martians have outwitted him and erased his memory. He has an underground base in the middle of the desert where he broadcasts his television show and dedicates his time to studying paranormal activity. Throughout most of the series, Stoat Muldoon is considered the antagonist of the show, but on a few special occasions, he joins forces with the Martians to defeat Emperor Bog and Dr. Damage. His name is a reference to another famous alien obsesser, Fox Mulder of the X-Files. He is not evil, merely over-eager. He was voiced by Robert Stack.
Dr. Damage - Bog's more intelligent right-hand-man, Damage constantly suspects that the Butt-Uglies are up to something. He's usually right, but rarely noticed. Damage (pronounced "dah-mahj") invents many instruments to try and win the conquest of Earth, but these usually lead to the Butt-Uglies destroying them and making Damage look like a fool in the process. He constantly insults Bog behind his back, despite Bog usually hearing him, and so always has to make up a compliment that sounds vaguely like what he was saying (e.g. "Royal nincompoop" becomes "loyal troops" in the first episode). He has also, on some occasions, tried to overthrow Emperor Bog as Martian emperor. However, Emperor Bog eventually found out about this ambition and, as Damage's punishment for his attempts to take over the position of Martian Emperor, made Damage wash and wax every ship on their base, and had Shaboom and Infi-Knight watch him to make sure that he did the job right.
Jax the Conqueror - A warlord who despises Martians, but after being defeated and imprisoned by B-Bop and the others pretends to be willing to help them invade Earth to get a chance for revenge. He pilots a ship called the Doom Jax which is impervious to Martian weaponry. He has been "destroyed" three times in the series run, but always manages to come back.
Humanga - A giant alien villain who is the only player of an alien game called Toget. Humanga has won as many games as the Butt-Uglies themselves.
Infi-Knight - A four-armed robotic warrior created by Damage to speed the Earth invasion along. Probably the Butt-Uglies' most powerful enemy. '''
Koofoo: - The last surviving member of an alien race. His race was an evil species that tried to conquer the whole universe. His crashed ship was submerged in the desert and believed to be a pyramid due to it's shape. Mudoon accidently released him at the same time the Martions arrived to destroy him. He took Angela to save her from danger but the Martions thought he was kidnapping her. It was eventualy revealed that Koofoo was not evil like the rest of his kind and had left the swarm of ships before crashing on earth. He says he doesn't want to fight or hurt anyone. The Martions do not believe him until Angela points out that they themselfes are different from almost all of their species. Koofoo leaves in peace. He reappears as a one - off at Do - Wah's birthday party in the comic serious.
Gorgon - A fire-breathing lizard-like alien characterized by the ability to change into or possess others and a TERRIBLE smell. He speaks with a hiss.
Klaktor - A Reconabot (portmanteau for "reconnaissance robot") that the Butt-Uglies defeated in the first episode, though he reappeared later in the series. Can fall apart and reassemble himself at will. This trait turned into a common sight gag; his action figure is equipped with ejectabe arms.