Marcus is an enthusiastic, cheerful boy who goes to Flatbrook High School. Despite being generally pleasent and friendly, he has trouble making friends due to being socially awkward and naive.

He comes from a poor religious family and is the oldest of four children. Much of his free-time is spent with his family, helping to care for his younger siblings. Whenever he's able to get away, he's usually found with Natalya Stonewall, who has been his closest friend since childhood. Recently, his parents have been increasingly concerned that he's been neglecting his religious studies, which they have blamed on his friendship with Natalya.

Mark is well-known for his obsession with childrens' cartoons - which gets him labeled him as "childish," "nerdy," and "weird." While Natalya usually joins in with teasing him on this interests, she has also gifted him much of the mercandise he owns, including the full DVD box set for his favorite cartoon.