Frank Vincent, Pesci and James Caan are probably the biggest mob groupies, as far as famous actors go. Anthony Quinn was another guy who had a relationship with a lot of gangsters. I know he was good friend of Frank Costello. Another guy many people tend to forget about is Marc Lawrence who played a lot of underworld characters. He's the guy who played Carlo Gambino in HBO's Gotti movie. Lawrence became very close to Lucky Luciano during Luciano's later years in Italy.