Chris is a successful actress and single mother living temporarily in Washington D.C. Despite her fame and wealth, she remains deeply devoted to her daughter. She is a pragmatic atheist who prefers logical solutions, but her desperation pushes her to seek unconventional help when medical science fails.

Regan is Chris's eleven-year-old daughter. She initially exhibits an artistic and intellectually inquisitive personality, showing great affection for her mother. Her severe deterioration becomes the central crisis for the household, prompting extensive medical and spiritual interventions.

Father Karras is a Jesuit priest and trained psychiatrist at Georgetown University. He comes from a background of severe poverty and carries profound guilt regarding his aging mother. Burdened by depression, he naturally seeks rational and scientific explanations for unexplainable phenomena.

A malevolent and cunning entity that invades the MacNeil home. It delights in psychological torture, using its ability to read minds to magnify the insecurities and grief of those attempting to intervene. It is profoundly arrogant and views its confrontation with human faith as an amusing game.

Father Merrin is an elderly priest and archeologist with previous experience combating evil in Africa. Having uncovered an ominous relic in the ruins of Nineveh, he carries a quiet, unwavering certitude about the spiritual battles ahead. He provides a strong contrast to his younger, more doubtful colleagues.

Burke is a British film director currently working with Chris on her latest movie. He functions as an alcoholic who frequently behaves abusively toward his crew, masking his insecurities behind a loud personality. Despite his volatile temper, he remains a trusted friend to the lead actress.

Detective Kinderman is a sharp, inquisitive homicide detective with a deep love for cinema. He hides his cunning investigative skills behind a rambling, eccentric demeanor. He slowly pieces together the bizarre clues surrounding the violent events occurring in Georgetown.

Karl is a middle-aged Swiss housekeeper working for the MacNeils alongside his wife. He is stoic and private, frequently bearing the brunt of Burke Dennings's drunken tirades while maintaining a fiercely protective stance toward his employers.

Willie is a Swiss housekeeper who works for Chris alongside her husband. She manages the day-to-day operations of the Georgetown home and provides a stable, comforting presence during the family's escalating crises.

Sharon is Chris's social secretary and Regan's personal tutor. She is deeply integrated into the MacNeil household, managing schedules and helping care for Regan as the young girl's condition grows increasingly unmanageable.

Dr. Klein is the primary physician Chris consults regarding Regan's erratic behavior. He represents the medical establishment's desperate attempt to apply physical diagnoses to an inexplicable condition, prescribing multiple tests and sedatives.

Father Dyer is a Jesuit priest and a supportive figure in Damien Karras's life. He frequently checks in on his friend, offering a listening ear and a bottle of scotch when Karras struggles with his personal demons.

Mary Jo is a Washington seer and medium whom Chris met at the White House. She is highly sensitive to the supernatural and becomes deeply unsettled by the strange energy in the MacNeil home.

Howard is Regan's father and Chris's former husband. He remains an absent figure whose lack of contact weighs heavily on Chris, fueling her fears regarding the emotional toll his neglect takes on their child.

Frank is the director of the Institute of Languages and Linguistics. He assists Karras by scientifically analyzing the strange voices recorded during Regan's episodes, identifying the hidden patterns in the speech.