Muhammad Ali was an American professional boxer, activist, entertainer and philanthropist. Nicknamed The Greatest, he is widely regarded as one of the most significant and celebrated sporting figures of the 20th century, frequently ranked as the best heavyweight boxer and greatest athlete of the century. He was involved in several historic boxing matches, most notably his fights with Joe Frazier and George Foreman. He has been ranked the greatest heavyweight boxer of all time, and as the greatest athlete of the 20th century by Sports Illustrated, the Sports Personality of the Century by the BBC, and the third greatest athlete of the 20th century by ESPN Sports Century.