In 1964, William Klein did what was then unthinkable: he made a film about a young black boxer by the name of Cassius Clay, a clownish upstart and deliberate provocateur when it came to issues of race and righteousness. Clay couldn't possibly beat heavyweight champ Sonny Liston, but he did, floating like a butterfly, stinging like a bee. A decade later, Klein returned for “The Rumble in the Jungle” as Clay, now Muhammad Ali, regained his title by defeating George Foreman. The road between these two bouts was fraught with upheaval: Ali was a self-generating spectacle of “greatness” who taunted white America, adopted Islam, refused the draft, and generally embodied the threat of a black man who wouldn't be counted out. For Klein, Ali personified a very American form of anarchic self-will. He reinvented himself, again and again, goading the media and making it ironically clear that as his fierce resistance grew, so did his stature. Muhammad Ali, the Greatest has the giddy and extravagant energy of its iconic fighter as it lands body blows to empire.