Ingenious portrayal of son (Al Pacino) to two different fathers.
Michael was torn between the elder (Marlon Brandon) and younger (Robert De Niro) Don Corleone in two of three acts, with Brando playing the elderly statesman while DeNiro had the more active "young dad" parts.
Timing was impeccable as Coppola captured Pacino stuck in the middle pulling off playing junior to a younger man (1940, 1943) in real life. Hollywood magic in the seventies was as simple as not having all three men in the same room at the same time.
My dad was a transporter at Special Surgery in Manhattan, when Brando came in on a stretcher. He said the guy was an asshole. Actually, he might have said the guy was arrogant.