Which entity is this text about?

Muhammad Ali (; born Cassius Marcellus Clay Jr.; January 17, 1942 - June 3, 2016) was an American professional boxer and activist. He is widely regarded as one of the most significant and celebrated sports figures of the 20th century. From early in his career, Ali was known as an inspiring, controversial, and polarizing figure both inside and outside the ring. Cassius Clay was born and raised in Louisville, Kentucky, and began training as an amateur boxer when he was 12 years old.

Clay made his professional debut on October 29, 1960, winning a six-round decision over Tunney Hunsaker. From then until the end of 1963, Clay amassed a record of 19-0 with 15 wins by knockout. He defeated boxers that included Tony Esperti, Jim Robinson, Donnie Fleeman, Alonzo Johnson, George Logan, Willi Besmanoff, LaMar Clark, Doug Jones and Henry Cooper. Clay also beat his former trainer and veteran boxer Archie Moore in a 1962 match.  These early fights were not without trials. Clay was knocked down both by Sonny Banks and Cooper. In the Cooper fight, Clay was floored by a left hook at the end of round four and was saved by the bell, going on to win in the predicted 5th round due to Cooper's severely cut eye. The fight with Doug Jones on March 13, 1963 was Clay's toughest fight during this stretch. The number-two and -three heavyweight contenders respectively, Clay and Jones fought on Jones' home turf at New York's Madison Square Garden. Jones staggered Clay in the first round, and the unanimous decision for Clay was greeted by boos and a rain of debris thrown into the ring (watching on closed-circuit TV, heavyweight champ Sonny Liston quipped that if he fought Clay he might get locked up for murder). The fight was later named "Fight of the Year" by The Ring magazine.  In each of these fights, Clay vocally belittled his opponents and vaunted his abilities. He called Jones "an ugly little man" and Cooper a "bum". He was embarrassed to get in the ring with Alex Miteff. Madison Square Garden was "too small for me". Clay's behavior provoked the ire of many boxing fans. His provocative and outlandish behavior in the ring was inspired by professional wrestler "Gorgeous George" Wagner. Ali stated in a 1969 interview with the Associated Press' Hubert Mizel that he met with Gorgeous George in Las Vegas in 1961 and that the wrestler inspired him to use wrestling jargon when he did interviews.  After Clay left Moore's camp in 1960, partially due to Clay's refusing to do chores such as dish-washing and sweeping, he hired Angelo Dundee, whom he had met in February 1957 during Ali's amateur career, to be his trainer. Around this time, Clay sought longtime idol Sugar Ray Robinson to be his manager, but was rebuffed.
Muhammad Ali