Constance Langdon is a key character. She has a deep connection to the Murder House. She's sort of like the keeper of the secrets of the house. She knows about the ghosts and the history of the murders that took place there. And she's always around, meddling in the affairs of those who enter the house.
Dr. Ben Harmon is another main character. As a psychiatrist, he tries to understand what's going on in the Murder House, but he gets drawn deeper into the horror. His attempts to fix his family while dealing with the supernatural elements of the house make him an important part of the story.