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Even if you've never heard of Rocco Musacchia, if you're a fan of gangster films like Prizzi's Honor, Donnie Brasco, and Mickey Blue Eyes, you're familiar with his work. Musacchia works as a 'technical advisor' on mob films. He teaches Hollywood actors how to act like gangsters. He grew up around such real-life characters in Brooklyn and has maintained his contacts over the years.
In the summer of 1989, Musacchia was working on The Freshman, starring Marlon Brando and Matthew Broderick. In the film, Brando parodies his role in The Godfather by playing a mobster named Carmine Sabatini, who just happens to look and even dress like The Godfather's Vito Corleone.
(thanks David)