25th February, 1964; Cassius Clay, defeated Sonny Liston when Liston retired at the end of the sixth round in Miami to become Heavyweight Champion of the World.

Muhammad Ali (born Cassius Marcellus Clay Jr.; January 17, 1942) is a retired American boxer and three-time World Heavyweight Champion, who is widely considered one of the greatest heavyweight championship boxers of all time. As an amateur, he won a gold medal in the light heavyweight division at the 1960 Summer Olympics in Rome. After turning professional, he went on to become the first boxer to win the lineal heavyweight championship three times.

Originally known as Cassius Clay, Ali changed his name after joining the Nation of Islam in 1964, subsequently converting to Sunni Islam in 1975. In 1967, Ali refused to be inducted into the U.S. military based on his religious beliefs and opposition to the Vietnam War. He was arrested and found guilty on draft evasion charges, 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 successful.

Nicknamed "The Greatest", Ali was involved in several historic boxing matches. Notable among these are three with rival Joe Frazier and one with George Foreman, whom he beat by knockout to win the world heavyweight title for the second time. He suffered only five losses (four decisions and one TKO by retirement from the bout) with no draws in his career, while amassing 56 wins (37 knockouts and 19 decisions). Ali was well known for his unorthodox fighting style, which he described as "float like a butterfly, sting like a bee", and employing techniques such as the rope-a-dope. He was also known for his pre-match hype, where he would "trash talk" opponents on television and in person some time before the match, often with rhymes. These personality quips, idioms along with an unorthodox fighting technique made him a cultural icon. In later life, Ali developed Parkinson's disease. In 1999, Ali was crowned "Sportsman of the Century" by Sports Illustrated and "Sports Personality of the Century" by the BBC.

Cassius Marcellus Clay Jr. was born on January 17, 1942, in Louisville, Kentucky. The elder of two boys, he was named after his father, Cassius Marcellus Clay, Sr., who was named for the 19th century abolitionist and politician of the same name. His father painted billboards and signs, and his mother, Odessa Grady Clay, was a household domestic. Although Cassius Sr. was a Methodist, he allowed Odessa to bring up both Cassius and his younger brother Rudolph "Rudy" Clay (later renamed Rahman Ali) as Baptists. He is a descendant of pre-Civil War era American slaves in the American South, and is predominantly of African-American descent with English and Irish ancestry.
 
Clay was first directed toward boxing by the white Louisville police officer and boxing coach Joe E. Martin, who encountered the 12-year-old fuming over the theft of his bicycle. However, without Martin's knowledge, Clay also began training with Fred Stoner, an African-American trainer working at the local community center. In this way, Clay could make $4 a week on Tomorrow's Champions, a local, weekly TV show that Martin hosted, while benefiting from the coaching of the more experienced Stoner, who continued working with Clay throughout his amateur career.

Under Stoner's guidance, Cassius Clay went on to win six Kentucky Golden Gloves titles, two national Golden Gloves titles, an Amateur Athletic Union National Title, and the Light Heavyweight gold medal in the 1960 Summer Olympics in Rome. Clay's amateur record was 100 wins with five losses.

Ali states (in his 1975 autobiography) that he threw his Olympic gold medal into the Ohio River after being refused service at a 'whites-only' restaurant, and fighting with a white gang. Whether this is true is still debated, although he was given a replacement medal at a basketball intermission during the 1996 Olympics in Atlanta, where he lit the torch to start the games.