In every generation there emerges a public figure who manages to dramatize the tensions, the aspirations, even the spirit of the epoch, and by so doing, define that era for posterity. Thus F. Scott Fitzgerald, the personification of the heady mixture of genius and new social possibilities played out in a very public manner, defined the Roaring Twenties. It is difficult to define how this process occurs, but when it happens it becomes obvious how ineluctably right the person is, how fated they are to play out the drama of their age; it appears that their ascendance is fated, so necessary that were the figure not existing, he or she would have to be created. Such was the impact of Muhammad Ali. Ali was a new kind of athlete, utterly divorced from the rags-to-riches saga of previous black boxers. By the close of the...