Donnie Brasco (1997)

New York, late 1970s: Lefty Ruggiero, a small-time gangster, works as a hit-man for the Bonanno crime family. When he meets the young Donnie Brasco, he is particularly impressed by his fearlessness. But he has no idea that Donnie's real name is Joe Pistone and that he is an FBI agent looking for a way to infiltrate the Mafia as an undercover operative. Lefty and Donnie become friends, and Lefty actually manages to convince the "family" to accept Donnie. The longer Joe Pistone investigates as Donnie Brasco, the more he changes, and step by step he identifies with his role in the mafia family. He increasingly neglects his own wife and children. Meanwhile, his relationship with Lefty, who treats him like a father, grows ever closer and more intimate. But the mafia bosses cannot be fooled forever. They soon discover that there must be a traitor among them. Joe Pistone, alias Donnie Brasco, finds himself forced to act.