Max is an unusually large twelve-year-old boy who struggles with severe shyness and a learning disability that makes reading difficult. Haunted by the memory of his mother's death and his physical resemblance to his imprisoned father, he isolates himself in his basement bedroom. Despite believing he lacks intelligence, he possesses strong observation skills and a gentle, compassionate nature.

Freak is a highly intelligent twelve-year-old boy born with Morquio syndrome, a condition that restricts his physical growth but leaves his intellect unaffected. He loves reading, science, and Arthurian legends, frequently framing his life as a series of knightly quests. He uses his sharp mind and commanding personality to compensate for his physical limitations.

Kenny "Killer" Kane is Max's father, an intimidating and massive man currently serving time in prison. His physical resemblance to Max creates constant tension in the boy's life. He possesses a manipulative, commanding presence and expects total obedience from those around him.

Gran is Max's grandmother, who shares custody of him following the death of her daughter. She deeply loves Max but harbors anxiety about his growing size and physical resemblance to his father. She tries to maintain a safe, predictable environment for her family.

Grim is Max's grandfather, a somewhat severe man who shoulders the responsibility of raising his grandson. He worries constantly that Max's physical growth is a sign he will inherit his father's dangerous traits. Despite his stern exterior, he acts out of a deep need to protect his family.

Gwen is Freak's mother, a beautiful and generous woman who works hard to provide for her son. She is extremely protective of Freak due to his severe physical disability and worries about his vulnerability. While initially frightened by Max's imposing size, she quickly recognizes his gentle nature.

Loretta Lee is a resident of the run-down "New Testaments" tenements. She struggles with alcohol and lives a hardscrabble life alongside her husband. Initially coming across as cruel and taunting, she possesses an underlying sense of conscience that occasionally surfaces.

Iggy Lee is the heavily tattooed, red-bearded leader of the Panheads motorcycle gang. He acts tough and intimidating toward children and those he views as weak. He quickly shifts into a cowardly, obedient servant when confronted by more dangerous individuals.

Mrs. Donelli is the eighth-grade English teacher assigned to instruct both Max and Freak. She struggles to understand the unusual dynamic between the two boys and often feels overwhelmed by their combined presence in her classroom. She genuinely tries to assess their learning through alternative methods.

Mrs. Addison is the prim, formal principal of the middle school. Despite her strict professional exterior, she possesses a sympathetic heart and worries deeply about the well-being of her students. She pays special attention to children with complicated home lives.

Dr. Spivak is a small, stern-faced physician who oversees Freak's medical care at the hospital's research wing. She is deeply familiar with Freak's condition and respects his intelligence. She treats him with honesty regarding his medical realities.

Tony D., known locally as Blade, is a seventeen-year-old delinquent who leads a dangerous street gang. He carries a reputation for violence and actively seeks out opportunities to intimidate and threaten younger or more vulnerable kids in the neighborhood.