Dr. Alan J. Hill is a psychiatrist who appears in interludes to the main plot of Until Dawn. He is portrayed by actor Peter Stormare.
During early psychiatry sessions, Hill asks the player to answer various questions about his or her fears, insecurities, and opinions about the action unfolding within the game. The answers to these questions are used to shape the way that the game unfolds.
As the plot of Until Dawn develops, Hill becomes progressively more critical of the subject's actions and the player switches from being a participant in the sessions to an observer.
References to Dr. Hill can also be observed in various clues accessible during the main plot of Until Dawn.
Source: Wikia Website.