However Ali was a controversial champion. In 1964 he threw his Olympic medal into a river to protest against racism in America. In the same year, he became a Muslim and changed his name from Cassius Clay to Muhammad Ali, He said that Cassius Clay was a 'slave name'. In 1967 he was sent to prison because he refused to fight in the Vietnam War. He said that the Vietnamese had never tried to hurt him, so he wouldn't fight them. Many of the things he said and did caused trouble and made him unpopular Even so, when he stopped boxing in 1981 he was stilling the world, 'I am the greatest!'