Back in 1964, America was just getting to know Cassius Clay, a brash 22-year-old from Louisville who four years earlier in Rome had won Olympic boxing gold.

But on Feb. 25, 1964 — 50 years ago today — the world would come to know "The Greatest."

That night in a packed Convention Hall in Miami Beach, Clay stood in the ring waiting for the reigning world heavyweight champ, Sonny Liston, to answer the bell for the seventh round of their title bout.

Instead, Liston threw in the towel, launching Clay — who would soon convert to Islam and change his name to Muhammad Ali — into international superstardom and status as one of the 20th century's most enduring cultural icons

"When Cassius Clay changed his name to Muhammad Ali, it became a newsworthy event that found its way onto the front pages," Thomas Hauser, author of "Muhammad Ali: His Life and Times," told FoxNews.com. "And the more important Ali became as a social, political and religious figure, the more important the fight became. If Cassius Clay hadn't beat Sonny Liston, the things he said and did afterwards wouldn't have had the same impact."

Six years later, Ali was perhaps the most recognizable man on the planet, a symbol of the anti-war movement, the equal of the sweet science's greatest fighters and a pioneer of the audacious, trash-talking style so prevalent in modern sports. Liston, in stark contrast, would be dead, a broken alcoholic whose suspected heroin overdose prompted rumors of a mob hit.

"... the more important Ali became as a social, political and religious figure, the more important the fight became. If Cassius Clay hadn't beat Sonny Liston, the things he said and did afterwards wouldn't have had the same impact."

— Thomas Hauser, author of "Muhammad Ali: His Life and Times

Prior to the bout, which was named the fourth-greatest sports moment of the 20th century by Sports Illustrated, the cocky young fighter from Louisville, Ky., had been favored by just 3 of 46 reporters. Liston, known as "Big Bear," boasted a record of 35-1 with 24 knockouts, and a glower that left opponents intimidated even before they entered the ring. But Clay, who was 19-0 as a pro, was anything but frightened.

READ: FBI suspected first Ali-Liston fight was rigged, documents show

"If you wanna lose your money, then bet on Sonny," Clay taunted before the fight, foreshadowing the maddening poetry he would use throughout his career to ridicule opponents, rendering them too angry to stick to their fight plans.

When the bell rang, Clay's blend of speed, footwork and power proved to be too much Liston. New York Times sportswriter Robert Lipsyte wrote that night that Clay had control of the fight from the beginning of the opening round.

“The tall, swift youngster, his hands carelessly low, backed away from Liston’s jabs, circled around Liston’s dangerous left hook and opened a nasty gash under Liston’s left eye,” Lipsyte wrote. “He never let Liston tie him up for short, brutal body punches, and although he faltered several times, he refused to allow himself to be cornered. His long left jab kept bouncing off Liston’s face. From the beginning, it was hard to believe.”

The 8,297 spectators at ringside for one of boxing’s most anticipated fights in years could not have known they were witnessing the birth of a legend. To this day, Ali, now 72 years old and addled by Parkinson's syndrome — brought on by blows to the head during a 20-year career that saw him win the heavyweight championship three times — remains arguably the sport's most beloved figure.

"Nobody had a clue that Clay was as good as he was or how great he would become," Hauser said. "Sonny Liston, at that point, was regarded by some people as possibly the greatest heavyweight of all time. He was thought of the way [Mike] Tyson was thought of before he was knocked out by Buster Douglas. He was Godzilla; he was going to reign for a thousand years."

Hauser, who interviewed more than 200 people for his best-selling book after being approached by Ali and his wife in 1988, said the initial bout undeniably changed history as the United States was still mourning the assassination of President John F. Kennedy just three months earlier.

"If Ali doesn't beat Sonny Liston, the course of history is different," he said. "It was the fact that he was heavyweight champion of the world that gave those acts on his part national importance."

Clay would later change his name to Muhammad Ali before the rematch with Liston on May 25, 1965, in Lewiston, Maine. The culmination of that match, which Ali won in the first round with a "phantom punch," resulted in one of the most iconic sports images of all time, as Ali stood over a fallen Liston while yelling: “Get up and fight, sucker!”

Three years later, Ali refused to be drafted for the Vietnam War, citing his religious beliefs. The U.S. government then refused to recognize him as a conscientious objector and Ali was eventually found guilty of draft evasion. He was ultimately stripped of his title and did not fight again for nearly four years until 1971, when his conviction was overturned by the U.S. Supreme Court on a technicality.

Ali later returned to ring on Oct. 26, 1970, defeating Jerry Quarry in three rounds. He went on to regain the title in 1974 and then again in 1978.