Greg is a talented sixth-grader at Ashworth Intermediate School with a lifelong passion for earning cash. Resourceful and heavily focused on his entrepreneurial goals, his latest venture involves writing, illustrating, and mass-producing miniature comic books to sell to his classmates. He keeps busy juggling odd jobs, sports, and schoolwork, though he frequently ignores the feelings of those around him in his pursuit of profit.

Maura is the girl who lives across the street from Greg and serves as his ongoing competition. She frequently copies his business ventures, moving from lemonade stands to her own handmade comic books. Underneath her combative exterior, she possesses a strong natural talent for drawing and storytelling, prioritizing artistic quality over sheer profit.

Anthony Zenotopoulous, widely known as Mr. Z, is a sixth-grade math teacher at Ashworth Intermediate School. He loves the stability of numbers and organizes his life around strict logical principles, calculating grades to three decimal places. Timid by nature, he has a profound physical aversion to blood that causes him to faint.

Mrs. Davenport is the firm but polite principal of Ashworth Intermediate School. She is highly protective of the school environment and strongly opposes the idea of students selling items on campus. She maintains traditional views on appropriate reading material, preferring classic literature over modern comic books.

Ross and Edward are Greg's older brothers. They are described as sloppy and frequently tease their younger brother about his intense focus on money and his interactions with girls. Despite their teasing, they occasionally rely on Greg for small cash loans, paying a mandatory fee for the privilege.

They are Greg's supportive parents. While they encourage his varied interests like sports and drawing, they sometimes worry that his drive to accumulate cash borders on an obsession. Mr. Kenton owns a large comic-book collection that helps inspire Greg's latest commercial venture.

They are Maura's parents, living across the street from the Kenton family. Mrs. Shaw is notably chatty and tends to recount family stories about minor injuries. Mr. Shaw harbors some initial reservations about Maura's business plans but generally supports her creative efforts.

Ted Kendall is a student at Ashworth Intermediate School. He assists Greg in selling the first batch of Chunky Comics, representing the broader student body's interest in buying and distributing items on campus.

Eileen is a student at Ashworth Intermediate School. She represents the typical middle-school social pressure that makes boys and girls hesitant to show friendliness toward one another, quick to point out any unusual socializing.

Brittany is a middle school student who notices Greg and Maura looking at drawings together. Her public teasing prompts Greg to defensively reject Maura's artwork to save face in front of his peers.

Allyson is a friend of Maura's at school. She is highly supportive of Maura's artistic endeavors and enthusiastically praises the quality of the unicorn comic book when she reads it, proving there is an audience for Maura's work.

Mrs. Jansen is a neighbor in Greg and Maura's community. She admires Maura's handmade potholders and happily purchases several of them, demonstrating to Greg that Maura has a viable business strategy and real sales skills.

Mrs. Emmet is the school nurse at Ashworth Intermediate School. She cleans Greg's bloody nose, applies a cold pack, and checks to ensure the injury isn't severe enough to be a break, providing practical care while the students sort out their conflict.

Mrs. Sanborn is the social studies teacher at Ashworth Intermediate School. She conducts an engaging, fast-paced class on history, demanding her students' full attention, which Greg struggles to provide when he is distracted by a note.