Ali's life has been recounted so many times that you'd think no one could come up with a fresh angle on it; documentary maker Bill Siegel (The Weather Underground) succeeds, primarily by delving into the religious story, largely downplayed by the mainstream, that's been sitting there in plain sight for 50 years. Siegel mostly dispenses with the fighter's comic pronouncements, his verbal jousting with Howard Cosell, in fact his entire athletic career, choosing instead to explore his great political awakening in the Nation of Islam. "I know the real God!" shouts 22-year-old Cassius Clay after beating Sonny Liston in 1963, and the statement defines him for the rest of the decade as he becomes a vocal advocate of black nationalism and sacrifices his heavyweight title to protest the racism of the Vietnam war. Minister Louis Farrakhan; journalist Salim Muwakkil; the fighter's second wife, Khalilah Camacho-Ali; and his brother, Rahaman Ali, all provide new insights into this remarkable world figure, who might have floated like a butterfly but whose social statements stung like a bee.