The thing about The Departed, the x-factor that people can't quite put their finger on, is that it deals clearly with class and accent all these things that are fundamental to Boston, but previously anomalous or even prohibited in demotic American films.

—- William Monahan, screenwriter for The 2006 film The Departed

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The movie is loosely based on the real-life Boston Winter Hill Gang; the character Colin Sullivan is based on the corrupt FBI agent John Connolly, while the character Frank Costello is based on Irish-American gangster and crime boss Whitey Bulger.