I and all the other males in my extended family were gathered around the radio when Cassius Clay fought heavily favored Sonny Liston for his first professional heavyweight title bout. The elders were all amazed when Clay scored his stunning first round knockout. Claims of a fix were widely made but never resolved. Whatever the truth of that match, I followed Clay, then later Ali, for the remainder of his career. He was the most important boxer I ever heard of, not just for his amazing speed, power and cunning in the ring, but also for his principled stand against the Vietnam war and draft which cost him years from his fighting prime.
It is ironic that the form of Islam he practiced, at least at the beginning, stood for separation of the races and religions. In later years, he is transformed into an almost universally admired and even unifying figure, despite the faux pas along the way.
I have also heard widely differing opinions on the effect of boxing on his subsequent Parkinson's disease.
Bottom line, Muhammad Ali's revolutionary effect upon professional sports, aided by media figures such as Howard Cosell, was such that there literally can never be another like him - a true legend