Which boxer was known as 'The Greatest'?

The boxer known as “The Greatest” was Muhammad Ali.

Ali adopted and popularized the nickname as part of the bold public persona that made him one of sport's most recognizable figures. Born Cassius Marcellus Clay Jr., he won Olympic light-heavyweight gold in 1960 and became world heavyweight champion by defeating Sonny Liston in 1964. Soon afterward, he announced his conversion to Islam and changed his name to Muhammad Ali.

Ali's nickname reflected both his extraordinary boxing ability and his willingness to promote himself with confidence. He combined speed, reflexes, movement, and unusual tactical intelligence for a heavyweight. His famous victories over Liston, Joe Frazier, and George Foreman helped turn the boast into a lasting sporting identity.

A common mix-up is confusing “The Greatest” with other boxing nicknames: Joe Louis was “the Brown Bomber,” Sugar Ray Robinson was “Sugar,” and Mike Tyson was “Iron Mike.” Ali also used “The People's Champion,” but “The Greatest” is the canonical answer to this question.