Originally Posted by Trojan
As I remember, Russo muscled his way in -- threatened Brando who thought he was acting -- to get the part

Gianni Russo had to battle Marlon Brando after snagging Carlo Rizzi role in “The Godfather”
Silive.com 03 October 2022

He’s [Carlo Rizzi] a central character in two of the most iconic scenes in what many consider to be the greatest film of all time, “The Godfather.”

According to Gianni Russo Extracts:
  • Battling Brando
But Gianni Russo, who played traitorous Carlo Rizzi in the film, had to go nose-to-nose with Vito Corleone himself, legendary actor Marlon Brando, before filming even began.

Russo had never acted before landing his role in the movie. Brando pressed Russo about his acting bona fides during an early rehearsal.
According to Russo, “He said, ‘Who’d you study with?’ I said, ‘Study what? What are you talking about?’”

Russo said Brando told director Francis Ford Coppola that he’d better re-think Russo’s casting.
“He’s trying to get me fired,” Russo said

Russo, who has his own lifelong familiarity with the mob, said he took Brando aside and out of earshot told the actor, “Listen to me, Mr. Brando, out of all due respect, you screw this up for me, if I get fired, I will suck on your heart. You will bleed out here today. If this guy fires me because of you, you’re dead.”
Brando, Russo said, stepped back and told him, “‘That was brilliant.’ He thought I was acting. I meant it.”

Brando later took Russo under his wing, helping him conceptualize the chilling scene where Michael tells Carlo that he’s is going to be exiled from the Corleone family only to have him whacked. “That’s Brando,” Russo said. “Brando was my only acting teacher.”