Ali had to face the greatest list of contenders. I can name most of them and anyone who lived back then probably can name the top 3 (Frazier, Foreman, and Norton). Larry Holmes era came next and he went undefeated, but I can't recall a big name he faced. Ali took a shot at Holmes, who was previously Ali's sparring partner, in a fight that should have been stopped. To this day I can't believe it wasn't. I believe it led to his deteriorating condition, but that's just me.
Ali WAS the greatest. He could slide (avoid) a punch better than anyone I have ever seen. From his brash fighting days, he became the world's most r cognizable face and became a fine ambassador for the US.
May he R.I.P.