1. Teddy Daniels: Teddy is the main protagonist and a U.S. Marshal investigating the disappearance of a patient from a psychiatric facility on Shutter Island. He believes he is on a genuine investigation, but it is later revealed that he is actually a patient at the facility suffering from a mental disorder.
2. Dr. John Cawley: Dr. Cawley is the head psychiatrist at the Shutter Island facility. He presents himself as a trustworthy authority figure but is eventually shown to be manipulative and deceptive, using experimental treatments on his patients.
3. Chuck Aule: Chuck is Teddy's partner in the investigation and appears to be a loyal colleague. However, it turns out that Chuck is part of the facility's staff and is assigned to monitor and control Teddy's actions.
4. Andrew Laeddis: Andrew is a patient at the facility who Teddy believes is the mastermind behind the disappearance of the missing patient. However, it is revealed that Andrew is Teddy's alter ego, a figment of his fractured mind, created by Dr. Cawley as part of an elaborate experiment.
5. Rachel Solando: Rachel is a mysterious patient at the facility whom Teddy encounters during his investigation. She claims to have important information about the island's secrets, but her existence and motives remain unclear throughout the film.
Ultimately, the movie's perspective shifts reveal that the events depicted may not be entirely accurate or objective, and the perceptions of the characters are often unreliable. The film leaves it up to the audience to interpret and decide who they believe is "right" based on the conflicting narratives and ambiguous nature of the story.