Muhammad Ali was an American professional boxer, activist, and philanthropist. Nicknamed The Greatest, he is widely regarded as one of the most significant and celebrated sports figures of the 20th century and one of the greatest boxers of all time.He was born and raised in Louisville, Kentucky, and began training as an amateur boxer when he was 12 years old. At age 18, he won a gold medal in the light heavyweight division at the 1960 Summer Olympics in Rome, then turned professional later that year, before converting to Islam after 1961. At age 22, in 1964, he won the world heavyweight championship from Sonny Liston in a major upset. He then changed his name from Cassius Clay, which he called his slave name, to Muhammad Ali.