James “Whitey” Bulger was practically a criminal from birth. His first arrest came at age fourteen, and his life was spent committing crimes and serving sentences from that point forward. One could likely form a compelling film about the man’s entire life.

Instead, Black Mass (2015) does not highlight the entire criminal life of Bulger, but starts around the late 1970s/early 1980s, at a time when Bulger’s most successful criminal enterprise was taking off in Boston. It was around these years he was appointed boss of the Winter Hill Gang, a successful Boston organized crime regime known for racketeering, loan sharking, and murdering rival mobsters to take over their business.

Not only is this time the most prominent in Bulger’s criminal history, it is also the era in which he served as an FBI informant, providing information that led to the downfall of the Patriarca crime family. In exchange for his information, the FBI largely ignored Bulger’s criminal activity.

Black Mass is based on the book by the same name, written by Dick Lehr and Gerard O’Neill, which focused on this same period of Bulger’s criminal life.