First things first, “The Departed” is a Warner Bros. remake of a 2002 Hong Kong movie called “Infernal Affairs” (via Variety). Much of the actual story and plot in “The Departed” is similar to “Infernal Affairs,” but adapted for American audiences. While “The Departed” is not necessarily based on a true story, Jack Nicholson’s character Frank Costello is based on real-life Boston gangster James “Whitey” Bulger, who led the infamous Winter Hill Gang out of Somerville, Massachusetts, in the late 20th century (via The Wrap).
In “Directors Close Up 2: Interviews with Directors Nominated for Best Film by the Directors Guild of America,” a compendium of interviews with Oscar-winning filmmakers, Scorsese told editor Jeremy Kagan that basing the character on Bulger was born from Nicholson’s desire to add “something a little more” to the typical gangster film, and that screenwriter William Monahan had the actual idea to base the character on Bulger. “Once we began to read the books on these people and the situation in Boston at that time, nothing that we did in the film was, in a sense, exaggerated in any way,” Scorsese said.
Like Nicholson’s character in “The Departed,” Bulger was also a real-life FBI informant who worked with corrupt FBI agents who helped cover up his crimes (via The American Conservative). While Nicholson’s character is killed midway through “The Departed,” Bulger fled Boston in 1994 and was finally arrested in Santa Monica, California, in June 2011 (via The LA Times). As reported by The Wrap, Bulger was murdered in prison on Oct. 30, 2018.