Robert De Niro met the real Ray Arcel around the time he appeared in Raging Bull (1980).
Frankie Carbo (John Turturro) is the real-life mob boss and boxing czar on whom the character "Tommy Como" was based in Raging Bull (1980).
During the height of his career, Roberto Duran was known to be very generous. Often handing out money to the poor in Panama. He saw himself as Robin Hood, helping the poor. Which is why he named one of his kids Robin.
The fourth movie in which Robert De Niro has appeared that has to do with boxing. The other three being Raging Bull (1980), Night and the City (1992), and Grudge Match (2013).
Roberto Duran owns a restaurant in Panama, where he's known for being prone to sing.