[Exhibitman]

Dave's analysis is a good one on the merits. I'd add only that from what his friend Sammy Luftspring wrote in his autobiography Marciano told him that he walked away in large part because he was sick of his management (Al Weill) stealing him blind on every purse and didn't want to take more beatings for small net money.

One other reason I'd add for his legendary status: ethnicity. It has always mattered in boxing when it comes to casual fans. Marciano was the last white American undisputed heavyweight champion. Ingo was a foreigner, and there were no white champs during the magnificent Ali-Frazier-Foreman-Norton era.