MARC’s not only the brain of the group he’s also in many ways the heart of the group. He’s the most sensitive spy, but being a guy, he tries his best not to show his emotional side in front of his brothers.
Marc is the smartest sibling on the team and is the 'family geek'. He also seems to be very sensitive, but tries to hide it from his brothers and almost everyone else. Marc is the smartest of WOOHP and his siblings, and even brags deeply about it to his siblings much of their annoyance. But, he also admitted that he really needs them in his life, except when Tony messes up his room, Megan hogs the bathroom, and Lee gives him atomic wedgies, in "Operation WOOCSI". When he tries to impress Sheena in "Operation Crabby Bob", Marc seems to be very nervous and is unable to tell a funny joke; when Sheena thinks he's creepy Marc seems to be deeply embarrassed and hurt. In the middle of the episode, Marc wants to change his appearance to be more 'cute' only to be caught by Megan. In the end of it Megan 'changes' his look to talk to her, Sheena says 'yes' to a date with him with Megan revealing that she hadn't changed his appearance with the gadget.
As he is a genius, Marc is very talented when it comes to thinking and figuring out puzzles. When Lee isn't present, he is usually the one to fly the jet, though this role is sometimes taken by Megan. His intelligence can be used in any type of situation, though he is very practical and never just jumps into something without thinking. Though he is very smart, sometimes he can be clueless; like in Episode 16 ("Operation Grow Up"), when he was examining a piece of cloth they found during their mission with his microscope and stated to his siblings he had been searching for hours and found no clue until Megan walked up to him and took the piece of cloth and pointed out and said, "Have you tried looking at the tag, genius?", Marc blushed at his mistake. In Episode 19 ("Operation Crabby Bob"), in the end of the episode, when Marc asked Sheena out and she agreed, Marc happily told Megan "Megan she said yes!! whatever look you picked worked!! Megan smiles and showed him mirror (one of their gadgets that changes your looks) Marc becomes shocked and said "No way" after he realizes his sister didn't change his look, Megan giggled and said to Marc "Go figure. You know for a genius, you can be pretty clueless sometimes".