There are aspects of the novel "The Godfather," and its film adaptation, that are based on or inspired by real-life events; for example, the novel's author, Mario Puzo, has described dealing with Frank Sinatra, who was angry that he served as the apparent inspiration for the "Godfather" character Johnny Fontaine. In both the novel and the movie, Fontaine is a popular singer with strong social ties to the mafia, and his story seems to have many parallels with Sinatra's, but Puzo was hesitant to confirm that the fictional popular singer with mob connections was actually based on the real-life popular singer with mob connections. In spite of Puzo's reticence to confirm suspicions, it seems unlikely that the fictional story was not inspired by real life, including instances in which Sinatra's career benefitted from mafia influence.
Other inspirations are much clearer. The famed gangster Meyer Lansky was a clear inspiration for the "Godfather" character Hyman Roth. Both Lansky and Roth were both wealthy, powerful Jewish men with mob connections and connections to Cuba, but the reference gets even more specific. The actor who played Hyman Roth, Lee Strasberg, has reported being praised by Lansky for his excellent portrayal, and in the film, Roth says something that Lansky himself said about his mafia activities: "We're going to be bigger than U.S. Steel."