I find myself in general agreement with Don Cardi's post, above, regarding Carlo Gambino being the "greatest" Mafia Don. He managed to insulate himself amazingly well, and certainly lived to a ripe old age - not something common in his line of work. So Gambino gets my vote as the Number One Greatest Don.
However, my vote for Number Two would have to be:
That's right,
Don Martin. One look at him, and you realize immediately where Vinny "The Chin" Gigante learned all he knew about acting "Mad." He had an excellent teacher, one who really managed to fly under the radar for a great many years and remained virtually unnoticed by the Feds.
Signor V.