It's not based on anybody, really. Puzo didn't know all that much about the mob. I think he lived in little italy in manhattan so he was very much aware of the mob's existance and the locally famous people in it, but he didn't really know anything specific about anything and just made all the people up based on what he saw/his experiences.
I'd have to disagree. Although Puzo presents us with a heavily-romanticized vision of the Mafia, it was published near the end of almost a decade of revelations about the real thing (e.g.
The Valachi Papers had finally been published just a year earlier), which is one of the reasons for
The Godfather's huge success - in 1969 the general public was morbidly fascinated by this shadowy underworld they'd all heard and read so much about over the past few years.
There's no doubt in my mind that Puzo was able to research the theme for his novel fairly thoroughly, including drawing on real mafiosi, past and present, for his characters: he just found 'the real thing' distinctly lacking for his purposes, so instead gave us the fascinating Corleone Family and their world.
