My knowledge of pro sports is fairly limited, but Muhammad Ali was a figure that guys my generation grew up with. He was the dominant star athlete of his generation.
i) On civil rights, he took a more confrontational approach than King. Although King's nonviolent philosophy proved to be a more effective strategy and tactic than the Black Panthers and the Nation of Islam, King's approach tended to foster a certain passivity. Get gov't involved, then let gov't solve the problem. Ali's individualism and self-reliance was admirable.
ii) He was one of the all-time great boxers. That raises the question of how to rank athletes. Let's take a few comparisons. It's easy to win a round of poker if you've been dealt a winning hand. More impressive is a player with a pair of clubs who can beat a player with a full house. How to turn a losing hand into a winning hand by successfully bluffing your opponent. How to win with nothing.
It's my impression that MMA fighters like B.J. Penn and Anderson da Silva have more natural talent than Rich Franklin. Something about their innate reflexes.
Not only does that make it easier to win, but when you have that much raw talent, the risk is to coast on your talent. By contrast, Franklin had to develop his full potential to be competitive. And he had to compensate by outthinking opponents.
Likewise, George Foreman was 7 years younger than Ali. In sports, that's a significant advantage. Since Ali couldn't outpunch Foreman, he had to outwit Foreman. Had to bring something to the game above and beyond physical ability. Had to use strategy. He conserved his energy while making Foreman expend his energy. Once Foreman's stamina was spent, Ali moved in for the kill.
In terms of absolute physical ability, Foreman might have been his superior, but Ali was able to adapt and compensate. By the same token, you have champs like Pete Sampras who excel despite physical impediments (thalassemia).
Compare that to, say, Michael Jordan. There's just something about his natural coordination that sets him apart. If you're ranking an athlete based on native ability, that's one criterion of greatness. If you're ranking an athlete based on factors that offset natural limitations, that's a different criterion of greatness.
iii) Apropos (ii), it's my impression that Ali changed technique. As a young boxer, he was fleet-footed. Very nimble. Later, he became more of a slugger.
It may be that the 5-year interruption in his career (the draft controversy) cut into his physical prime, and by the time he returned, he lost his youthful edge, so he had to retool. A man's physical prime is narrow. An athlete's physical prime is narrower, because he pushes himself to the limit. A champion's physical prime is even narrow because he must be at peak performance to beat the best.
iv) Apropos (iii), who's the greater champion–an undefeated champion, or a champion who comes roaring back after defeat? Some champs are unstoppable until they are stopped, and they never rebound. They never regain their former momentum, viz. Mike Tyson, Tiger Woods, Brock Lesnar.
v) In some ways, he was not an admirable person. Ali was very promiscuous. And he betrayed Joe Frazier's friendship. Ali could be competitive to a fault. Sacrificing things that are more important for his almighty career.
vi) Of course, one thing that set Ali apart was his witty, charming personality. The catchy one-liners. Take the classic interviews with Howard Cosell. The mock aggression. The quick, clever repartee.
vii) How far you can fall depends on how high you are. There's the drastic contrast between Ali in his prime and the shell of a man after dementia pugilistica hollowed out his physical and mental health. The brain damage robbed him of the very things that made him a star. Gone were the quips. Gone the physique. Gone the indomitable spirit.
Aging and illness are the great levelers. The most talented, brilliant, or beautiful people are still mere mortals, like the rest of us. If they live long enough, they will be reduced to utterly ordinary people, dependent on the mercy of others. Like Nebuchadnezzar, Ali was arrogant and boastful. Like Nebuchadnezzar, illness demoted Ali's pride and pretensions. From "the Greatest" to a helpless, pitiful figure. Not a Christian, he had nothing to fall back on when his body gave out.