Martin is just like any other 16-year-old, and has a wild passion for the paranormal. But after unwillingly solving an amazing "out of this world" mystery, he finds himself working as a paranormal investigator for "The Center". As the leader of the trio, Martin is also the only one who wears a U-Watch. Martin's first monster was Venoso, a female chameleon-like monster that has the power to shape shift into any person it wants.
Martin's appearance was considered and shown as slender with fair skin, yellow spiky hair and with brown eyes. His main outfit in every episode is wearing a red and yellow collared shirt with a white and slate blue bordered (on the top) shirt in it (on most episodes) and a black long-sleeved shirt in it (on episodes occasionally), tan-grey pants with red and white sneakers with white shoelaces.
in season 4, his appearance has change considered and shown as buff, muscular and beefier.
Whether he is at school or on a mission, he always remains the same outrageous, immature and hyperactive nerd, constantly bursting with energy. He seldom thinks before leaping into danger, even if it is to help someone in peril whenever they are on a mission, Martin always jumps to conclusions and comes up with every unlikely theory he can think of, usually from some movie he saw or from his subscription to "Paranormal Monthly".
Martin has a peculiar love for everything slimy, sloppy, and gooey - things that make Diana gag. His favorite hobby is teasing Diana by playing pranks and creeping her out, even though she often retaliates with physical abuse. A running gag in the series is Martin's constant flirting with every beautiful girl he meets, who usually reject him with verbal or (in Jenni's case) physical abuse.
Gerard Mystery is Martin's father and Diana's stepfather. He is a rational and logical scientist who spends most of his time in the scientific field. Unlike his son, he considers anything related to the paranormal "balderdash". But in the eighth episode from Season 3, Wrath of the Torrington Worm, he finds out about the center and is sworn to secrecy.
Diana Lombard is Martin's stepsister and usually the person who is the target of most of his pranks. She is serious, rational, and a straight A student, like the exact opposite of her step brother. Unlike Martin, every time on a mission, she tries to rationalize everything stating that it is local even the things that are to straighten up paranormalists. Diana has the hardest time keeping her cool and her temper around Martin when he makes fun of her and scares her causing her to slap, punch, kick or strike him with physical abuse. She works at The Center with Martin and is part of the team.
Jenni is Martin's unrequited love interest, she views Martin as immature based on the pranks he pulls on Diana and other students and calls him a "Freak" and most of the time a "Loser". But there are sometimes where Jenni seems interested in Martin because he acts like a gentleman but has no memory of most of it. Her memory was erased because paranormal ties to the time of her interest. Jenni is not seen for a semester at Torrington because she moves but it is not clearly stated.
A girl who very similar to Martin and seems to be interested in everything he likes. She likes the paranormal, monster movies, and comic books just like Martin. She was Martin's girlfriend for a brief amount of time before she dumps him because he missed a date with her because he was fighting a Djini that was driven by revenge.
Marvin is Marin's rival through out the series. He seems to be a parallel in almost every way and yet similar at the same time. He wears shirts with the same pattern as Martin, skateboards like Martin, and even has a comic book series about him being a paranormal investigator.
He meets the "Totally Spies" in an episode crossover, "Totally Mystery Much?," investigating in the same case (Unfortunately Diana and Java are absent and weren't involved in this episode for some reason). In the end of the episode, Alex and Martin end up liking each other because they both have common interests in video games. Unfortunately, Martin was called in by The Center to work on another paranormal case.
The spies were obligated by Jerry (Their boss that works at an organization similar to The Center but called WOOHP, a.k.a World Organization of Human Protection) to team up with Martin to solve the case. He believes that Sam is like his sister Diana, he refers to both of them as "buzzkills."
- Martin has a large scar on his left leg that he got from the Mothman. He also has one on his stomach on the left side from a Spider Beast he encountered in an off screen incident.
- In the pilot episode, Martin's pants were originally going to be pink.