muhammad ali. [video clip] >> he is 22 years old. and he is standing up to the whole establishment. david: why did you decide to focus on muhammad ali? what was your interest in him? ken: well, he is one of the most compelling figures in american history. he certainly intersects with all the major issues of the last half of the 20th century. the role of sports in society, the role of the black athlete in sports, the definitions of black manhood and black masculinity and the civil rights movement. not as a fixed thing, but as an ongoing developing thing. the story of politics, of race. the central american question. freedom. it is also about faith and religion and islam, about sex and all these things because human nature does not change. or things we are grappling with today. when you have a larger-than-life mythic figure like ali, he just lights up page after page of history. he is irresistible and is a way to communicate some complex undertow about not just the u.s. but who we are. david: how long did it take you to do that series? ken: we said yes to this in 2013. we began work in 2014. real earnest production and shooting of most of the stuff began in 2016, the year he died. so you could say that it took eight years or seven years but, you know, there is fundraising involved, there are other projects that you're giving your attention to at different times. what we need is that period of time to do the research, to do the deep dive on the archives and to be able to come up and say we think we really got him, or at least that we have materials that show the kind of dynamics and the dimensions, the contradictions, even the controversies, the flaws of a character and not have it merely be a resuscitation of conventional wisdom. david: so when muhammadli -- did you initially seek his approval or his family's approval or not? ken: no, we never operate that way. we can't operate that way in pbs because we so completely, we have to have a separation of church and state. we did have cooperation from family members in that they gave the photographs, they gave us access. we were able to interview two of his ex-wives. we interviewed two of his daughters, his brother, friends, family, hangers on, scholars. all of that sort of stuff, the kind of triangulation we want to do. david: when you see boxers today, professional boxers, they seem awfully bulked up. they have muscles, maybe because of stimulants they are taking or they have better training, but he did not seem like an overly muscular person. what was his strength as a fighter? was he as fast as anybody else? what was it that made him such a great boxer? it was not because he was so strong, was it? ken: well, he trained. he was very, very disciplined most of his life. he usually lost w