When Jonathan Eig realized there hadn’t been a biography on Muhammad Ali’s entire life, he knew he found his next project. With other books on Al Capone, Lou Gehrig, and Jackie Robinson under his belt, he felt confident in his task, but also didn’t know anyone in the world of boxing to begin.

Eventually, Eig was able to launch conversations with the key people from Ali’s life, including his three surviving wives and past managers. Conducting over 500 interviews to gather information for the unauthorized biography, he even uncovered thousands of pages of unreleased FBI and Justice Department files on one of the most popular men of all time. Now he’s working with Ken Burns on an official documentary series.

In this interview, Eig shares the role of “happy accidents” in the life of Muhammad Ali, his views on the value of biographies and autobiographies, how he determines fact from fiction in his research, why a massive index is crucial, and he shares a few details about his next challenge, a biography on Martin Luther King, Jr.

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