The most likely source of inspiration for Vito Corleone is Joseph Bonanno, for various reasons
First, like Vito, was a young Mafia boss and gave his name to the family,
Second, made and then tried to make boss his son Bill, sparking the famous banana war in the late 60s
Third he was apparently contrary to the drugs, but actually did a lot of business with heroin and sent to deal Carmine Galante,
Fourth; in a scene Sonny says, that''there are 100 men on the streets''; the Bonannos have always been small for this Joe had alliance with his cousin Joe Magaddino from Buffalo
Fifht, as Vito, he was born in Sicily.