The boxing legend Muhammad Ali has died aged 74. He was in hospital with breathing problems. People say he is the best boxer ever. He was world heavyweight champion three times. His nickname is 'The Greatest'. He was a civil rights and anti-war hero. He also worked for world peace for 50 years.

World leaders and famous people talked about Ali. One said Ali changed the world and that his work, "will be part of our history for all time." The U.N. Secretary-General said Ali fought for a better world. Ali said: "I would like to be remembered as a man…who treated everyone right [and] tried to unite all humankind."