A brave and intelligent 18-year-old living outside Incarceron, daughter of the Warden, who grapples with the demands placed on her in a corrupt society. Her curiosity and defiance drive much of her actions throughout the narrative.

Finn's oathbrother and fellow inmate, who is charming but untrustworthy and adheres to a self-serving philosophy. Despite his duplicitous nature, he shows moments of loyalty, particularly towards Finn.

The Warden of Incarceron and Claudia's adoptive father, who is embroiled in political machinations and the concealment of Incarceron's true nature. He has a dual role both outside the prison and as a character within its walls.

Claudia’s private tutor and a Sapient who aids her in her endeavors with his knowledge and access to forbidden technologies. He serves as a moral and intellectual guide for Claudia.

Queen Sia is a mysterious and manipulative ruler focused on securing the throne for her biological son Caspar, who is engaged to Claudia but lacks leadership qualities. Their familial ambitions create tensions central to the story.

An inmate and Sapient whose scholarly pursuits in Incarceron drive his curiosity about the outside world. His beliefs in legends lead his actions, albeit sometimes to misguided conclusions.

A resourceful inmate who initially hides her identity for safety but becomes a loyal ally to Finn. Her survival skills and insights contribute significantly to the group's efforts.