Ken Burns' 'Muhammad Ali' documentary, premiering September 19 on PBS, is as thorough as it is fascinating.

Muhammad Ali, born Cassius Clay on Jan. 17, 1942, is regarded as one of the top professional boxers of all time. He was an activist who spent his life fighting for and enacting change.

The making of a champion: Ali’s early years American Heavyweight boxer, Cassius Clay (later Muhammad Ali, 1942 – 2016), making a fist as he lies on his hotel bed, London, 27th May 1963.

Foreman attended Ali's memorial and funeral service when Ali died in 2016. But the relationship got off to a rocky start in 1974 leading up to "The Rumble in the Jungle,'' their fight in Zaire.