The show takes place in a small calm town named Single Town. Single Town is two hundred years old and was founded by a man named Addison Single (who was really an alien disguised as a human). Unbeknownst to its human inhabitants, Single Town is actually a meeting place for aliens from different parts of the galaxy.
Cathy Smith (Cath) (Voiced by Andrea Libman) - Cathy appears to be a bubbly, 12-year-old girl in the earth, equivalent to 700 Rhapsodian years, because she's an alien from the planet Rhapsodia. She came to Earth with her grandfather, Mr. Smith, to start the Monster Buster Club. She is constantly surprised at how different Earth is from Rhapsodia. She has many alien abilities, including the ability to stretch, and slight telekinesis. She is the most optimistic of the MBC. Her suit color is pink. In her chosen human form, she has blond hair and blue eyes. Her Rhapsodian form is shown to be a humanoid, white alien with scattered pink spots, with four tentacles for arms, and four tentacles for legs, as well as tentacles on her head, (like hair), and a long, furry-looking tail[1] Compared to humans, Rhapsodians are extremely long-lived.[2]
Chris (Christopher[3]) (Voiced by Sam Vincent) - Chris is the 12-year-old tech-guy of the group. He has indigo blue hair and dark blue eyes. He is very smart, with a knack for gadgets. He'll often stay back in the clubhouse and supply intelligence reports while the rest of the group is out on a mission. His suit color is blue.
Sam (Samantha) (Voiced by Anna Cummer) - Samantha, known by her friends as Sam, is an African-American girl with an often serious disposition. She has dark hair tied in Pony buns and hazel eyes. While officially the MBC has no leader, she'll often make attack strategies and plans for the group. She, at times, can be bossy. While she is a great unofficial leader she'll often put MBC first instead of having fun. Her suit color is yellow.
Danny (Daniel Jackson[4]) (Voiced by Matt Hill) - Danny is 12 year old boy and a nice guy at heart. He's good at sports, He has brown hair, green eyes and a scar over his left eyebrow. He can get a little overconfident at times. He has a crush on his schoolmate, Wendy. He is very popular at school and is always invited to all sorts of parties. He has a good sense of humor and likes cracking jokes even in dangerous situations. He has his own nickname "The Danny" and calls it himself whenever he's doing his task. His suit color is red.
Mr. Hugo Smith (Voiced by Ian Corlett) - Mr. Smith is Cathy's aloof grandfather and came with her to Earth. Like Cathy, he is a Rhapsodian, but rarely displays any supernatural powers and his alien form has the appearance of a mollusk. He'll sometimes aid the MBC from the clubhouse, but often he won't be involved in their missions at all. Mr. Smith loves working in his garden and playing cards with his plants.
John - John is Chris' little brother. He sometimes takes over for Chris at the clubhouse when Chris is on a mission or busy. He really wants to be in the MBC but he's too young as this is shown in the episode "Monster Beaters" where he joins another monster busting group because the MBC won't let him join.
Wendy (Voiced by Tabitha St. Germain) - Danny's crush who is the snobby girl at the school which the MBC attend and often makes fun of them. She also uses Danny to do things for her, which is seen in "Dog Daze" where she asks him to watch her dog Matise. She is known for gossiping and tries anything to get a good scoop. (This is shown in the episode "Bubbleheads" when she follows Cathy to Mark's house because she thinks Cathy's working on another story.)
Mark - Danny's main rival who often challenges him at different activities. Mark is also the richest kid in town. He likes to brag about it. He uses his money to beat Danny at things (shown in "Bubbleheads") or to become popular at school. Mark has a huge crush on Wendy as well.
Jeremy Flablotnick - Chris' computer club pal who often bothers Cathy because he's in love with Cathy. (Jeremy sometimes gets in the way of the MBC's missions, this is shown in the episode "The Forget Me Stone".) Jeremy is clueless when he sees the MBC in their suits as shown in the episode "Gotta Dance" when he thinks he's on a hidden camera show.
Elton Smith - Cathy's mind-reading cousin. He is wanted by the PincerBots for his mindreading powers. This is shown in the episode "Mindreader". His suit color is green.In "The End of Everything Part 2" he was the sub MBC member for Cathy.
Ralph - One of Mark's friends who Mark often uses to bring him things and uses him to help get back at Danny. Ralph also has a crush on Wendy.
Roy - Mark's other friend who he uses to bring him things[5] and who he also uses to help get back at Danny (shown in the episode "Snack Time").
Gilbert - An alien disguised as a nerd who hypnotized people including Sam to collect his comic book collections[6]. He also caused trouble in episode "Laugh Attack" with a Ha Ha Honker.
Mr. Fusster - The MBC's science teacher who thinks aliens don't exist. This upsets Cathy who knows that aliens exist and often argues with him. This gets her in trouble (shown in the episode "The Trouble with Troublemaking", when Cathy gets angry and pushes all his books off his desk getting her a detention). Recent events, though, show that he may know more about aliens than he lets on, and may even be one.
Principal Rollins - The gang's principal who thinks the students are soldiers and often uses terms like "Company halt!" and "About face!". She sometimes gets in the way of the MBC's missions this is shown in the episode "Monster Beaters" when she forces every student to join a school club (leaving the MBC little time to investigate). She has shown in various episodes an affection for Mr. Smith. It is also suggested she used to be a spy, and believes Cathy is one too.
