Donnie Brasco (1997)

This drama about an undercover cop who learns the hidden dangers of working his way inside the mob was based on a true story. Joe Pistone (Johnny Depp) is an FBI agent who is given an assignment to infiltrate the Mafia; calling himself Donnie Brasco, he befriends Lefty Ruggiero (Al Pacino), a low-level mob hit man whose personal life is in tatters. Lefty's marriage is falling apart, his son is a junkie, and his health is failing, which only adds to his growing disillusionment about having spent 30 years with the Mafia (and killing 26 people) with little to show for it...