In 1962, boxing writers and fans considered Cassius Clay an obnoxious self-promoter, and few believed that he would become the heavyweight champion of the world. But Malcolm X, the most famous minister in the Nation of Islam--a sect many white Americans deemed a hate cult--saw the potential in Clay, not just for boxing greatness, but as a means of spreading the Nation's message. The two became fast friends, keeping their interactions secret from the press for fear of jeopardizing Clay's career. Clay began living a double life--a patriotic "good Negro" in public, and a radical reformer behind...