It is interesting to note that the real life mob figure Meyer Lansky, who Hyman Roth is based off of in Part II, was forced to agree to a hit on his friend Bugsy Siegel, who Moe Green is based off of in Part I, for continuing to lose the mafia's money invested in the casino. And then in Part II, they make up their own story that Roth has a grudge against Michale and the Corleone Family for having his good friend killed. And here is this famous quote by Lansky.

"If it was in my power to see Benny alive. He would live as long as Mathusala."