Muhammad Ali (born Cassius Marcellus Clay, Jr. January 17, 1942) is an American former professional boxer, philanthropist and social activist. Considered a cultural icon, Ali has both been idolized and vilified.

Originally known as Cassius Clay, at the age of 22 he won the world heavyweight championship from Sonny Liston. Ali changed his name after joining the Nation of Islam in 1964, subsequently converting to Sunni Islam in 1975. In 1967, three years after Ali had won the heavyweight championship, he was publicly vilified for his refusal to be conscripted into the U.S. military, based on his religious beliefs and opposition to the Vietnam War. His 1966 statement, "Man, I ain't got no quarrel with them Viet Cong", was one of the more telling remarks of that era.

Ali was eventually arrested and found guilty on draft evasion charges; he was stripped of his boxing title, and his boxing license was suspended. He was not imprisoned, but did not fight again for nearly four years while his appeal worked its way up to the U.S. Supreme Court, where it was eventually successful.

Ali would go on to become the first and only three-time lineal World Heavyweight Champion.

Nicknamed "The Greatest," Ali was involved in several historic boxing matches. Notable among these were three with rival Joe Frazier, which are considered among the greatest in boxing history, and one with George Foreman, where he finally regained his stripped titles seven years later. Ali was well known for his unorthodox fighting style, epitomized by his catchphrase "float like a butterfly, sting like a bee", and employing techniques such as the Ali Shuffle and the rope-a-dope. Ali brought beauty and grace to the most uncompromising of sports and through the wonderful excesses of skill and character, he became the most famous athlete in the world. He was also known for his pre-match hype, where he would "trash talk" opponents, often with rhymes.