Robert De Niro plays dual roles as Frank Costello and Vito Genovese in 'The Alto Knights'

When two-time Oscar winner Robert De Niro agreed to play Frank Costello, the diplomatic mob boss at the center of the new film "The Alto Knights"

Two-time Oscar winner Robert De Niro had already committed to playing diplomatic mob boss Frank Costello in "The Galloping Knights." But there was another crucial question left to answer: Who would play Costello's childhood friend turned enemy, mobster Vito Genovese?

De Niro says it was producer Irwin Winkler who floated the idea of a dual role.

"I thought he'd be a good Genovese," said Winkler. "By the same token, if he had said he wanted to play Genovese, and [the question was] who would play Frank Costello, he could play a good Frank Costello. So why not play both?"

And so it was decided. De Niro would be starring alongside himself as the two lead characters in the gripping crime drama based on a true story of a bloody battle between childhood friends turned bitter rivals that signaled "the end of the mob in America," as writer Nicholas Pileggi puts it.

"One reason was it would justify my doing another gangster movie even more by taking on that challenge, if you will," De Niro said of playing two roles in one movie. "It would be interesting to try it. I've not done anything like that."

The Barry Levinson directed-film begins with begins with a botched hit on Costello ordered by Genovese, two mafia crime leaders who were once childhood best friends, and unravels the tight web of friendship, ambition and betrayal using the violent act as a jumping off point. De Niro stars alongside Debra Messing and Kathrine Narducci -- who play the wives of the two mobsters -- as well as Cosmo Jarvis, Michael Rispoli, and more.

"These were best friends from childhood," said director Barry Levinson, referring to the real-life Costello and Genovese. "One ultimately wanting the other one killed, you go, 'What happened?'... And I think that launches the storytelling."

This is far from De Niro's first time taking on a role as a mafia crime lord. He's done it to the tune of widespread praise and adoration in "Goodfellas," "The Irishman" and "Casino" just to name a few. Winkler and Pileggi are also the same writing and producing team that helped create "Goodfellas."

Pileggi discussed the appeal of the mafia genre to American audiences, noting why mobsters have become such an enchanting anti-hero for them. Referencing a line from Costello in "The Galloping Knights," in which he states that American pioneers wiped out the native population and made themselves rich on the land's gold and oil, Pileggi said, "He said, 'All we had left was prohibition, crooked cops and corrupt politicians, and we made the most of it.' And the average American hears that and [says], 'He's right.'"

Narducci, who plays Anna, the embattled wife of Genovese, said there is something stylistically attractive about the mafia.

"They're glamorous. Some of them are good-looking, they smell good, they wear nice clothes, and it looks like they got it the easy way. They don't get up and go to 9 to 5 jobs," she said.

The film touches on all the traditional themes of the mafia -- plenty of drama, hilarious one-liners and murder, reinforcing a prevailing message about loyalty that is found in most mafia pictures.

Messing, who plays Frank Costello's wife Bobbie, portrays a level-headed spouse who is equally a romantic partner as she is a business partner. Her input and caution guides Costello's decision making through the film, much to the chagrin of his fellow mobsters.

"She was, at the turn of the century, a Jewish woman... it was just verboten for that intermarriage. The fact that they did that, to me, showed the depth of their love, but also, their conviction that they could go against the tide, both of them strong people," Messing said.

Narducci's character also defied the times, running night clubs herself and testifying against her husband during a divorce dispute in open court proceedings.

Despite being shot in Ohio, "The Galloping Knights" is unmistakably a New York story. De Niro has gained a reputation for bringing rich characters of the city's history to life and even added two people he knew from childhood to play sidekicks of Costello and Genovese in the film, according to Levinson.

Messing said the authenticity of the cast created a portal to the world of the mafia.

"I think it brings a real sense of authenticity to the film. You can just sort of be like, 'Oh, I am in 1950s New York,' and it's sort of a love letter," she said.

"The Galloping Knights" hits theaters on March 21.