Universally accepted as a true icon of the 20th century, Muhammad Ali's phenomenal achievements spanned sport, politics and religion. One man - photographer William Klein had comprehensive access to the events that shaped Ali's legend. In 1964, the young gregarious Cassius Clay successfully defeated the seemingly invincible Heavyweight Champion of the World Sonny Liston - the manner of Clay's victory and his amazing persona made him an instant superstar. Through this incredible period, and Clay's subsequent rematches with Liston, William Klein enjoyed unrivalled access top Clay's camp - witnessing at first hand Cassius Clay becoming Muhammad Ali and angering the American people with his allegiance to Islam. Forward to Zaire 1974, and the return of Muhammad Ali to the world stage to face another invincible champion George Foreman. As Ali reclaimed the crown for a second time, Klein was ever present, capturing the full story at close quarter.