Jack Nicholson's character in The Departed was actually based on a real-life gangster. Watch the trailer below:

Martin Scorsese's 2006 epic crime-thriller picked up four Oscars at the 79th Academy Awards and for those unaware of the film, the official synopsis reads: "An undercover agent (Matt Damon) and a spy (Leonardo DiCaprio) constantly try to counter-attack each other in order to save themselves from being exposed in front of the authorities.