The word iconic is badly overused these days, especially by lazy journalists, but it can applied with calm accuracy to this man. As much as John Lennon, John F. Kennedy, Pelé, or anyone else from that era, Ali was an icon of the sixties.
Here's a little anecdote, for what it's worth. In 1975-76 I backpacked through Africa for about a year. It changed my life, but that's another story. Ali's bout with Foreman in Kinshasa was only a few months in the past. What absolutely gobsmacked me was that everywhere I went — literally every country, and I covered thousands of miles — the entire continent was in an extended honeymoon with this man. Not simply for what he did in Kinshasa (which was of sport's minor miracles in itself, see on that Norman Mailer's book, The Fight) but just as important, the fact that he had taken on the might of the American state and the military machine and stood his ground, even at the cost of his title and his profession, in refusing to fight in Vietman. As he said himself so aptly, "No Vietnamese ever called me ******". I would go into the smallest houses, indeed shacks, invited in by African hospitality, and there would be some photo of him that had been ripped out of a magazine tacked up on the wall. I've never seen that of any other figure, sporting or otherwise.
Now he was no saint, and he knew it. He didn't care about that. "He was a man, take him for all in all. We shall not look upon his like again."
HIghly recommended: Mike Marqusee's fine book, Redemption Song: Muhammed Ali and the Spirit of the Sixties. Not an exercise in servile hagiography, far from it. Just putting the man back into his times.