A seasoned U.S. Marshal and World War II veteran who travels to Shutter Island to investigate the disappearance of a patient. Haunted by the tragic death of his wife and his wartime experiences, he is a sharp but troubled investigator suspicious of the hospital's methods.

Teddy's new partner, a U.S. Marshal recently transferred from the Seattle bureau. He is amiable and supportive, quickly building a rapport with Teddy as they navigate the island's hostile environment.

The psychiatrist-in-chief and head of Ashecliffe Hospital, known for his intelligence and progressive views on treating the criminally insane. Despite his seemingly cooperative demeanor, he appears guarded and controls the flow of information regarding the hospital's operations.

A patient at Ashecliffe Hospital who was committed after drowning her three children, an act for which she refuses to accept reality. Her mysterious escape from a locked room acts as the catalyst for the Marshals' investigation.

Teddy Daniels' deceased wife, who died in an apartment fire two years prior to the story's beginning. Although not physically present, she is a central figure in Teddy's psyche, appearing frequently in his dreams and memories.

A former maintenance man and pyromaniac whom Teddy believes is responsible for setting the fire that killed his wife. He is the primary target of Teddy's personal vendetta and is believed to be incarcerated somewhere within Ashecliffe's walls.