In 1971, both Muhammad Ali and Joe Frazier were undefeated champions (in Ali's case, actually, former champion) who held legitimate claims to the title of "World Heavyweight Champion". Ali had won the title from Sonny Liston in Miami Beach in 1964, and successfully defended his belt up until he had it stripped by boxing authorities for refusing induction into the armed forces in 1967 (though he was still recognized as the Lineal heavyweight champion). In Ali's absence, Frazier won two championship belts, knocking out Buster Mathis for recognition as champion in five states (most notably, New York) and Jimmy Ellis, who had won the World Boxing Association's world title by winning a WBA elimination tournament, to replace Ali as the acknowledged, unified world champion. Frazier was plausibly Ali's equal, which created a tremendous amount of hype and anticipation for a match pitting the two undefeated fighters against one another to decide who was the true heavyweight champ.

Ringside seats were $150 (equivalent to $1,129 in 2023) and each man was guaranteed $2.5 million. In addition to the millions who watched on closed-circuit broadcast screens around the world, Madison Square Garden was packed with a sell-out crowd of 20,455 that provided a gate of $1.5 million (equivalent to $11,285,127 in 2023).

Prior to his enforced layoff, Ali had displayed uncommon speed and agility for a man of his size. He had dominated most of his opponents to the point that he had often predicted the round in which he would knock his opponent out. In October 1970, he stopped Jerry Quarry via cuts after three rounds in his first match after a three-and-a-half-year layoff. However, in his next fight, the last preceding the Frazier fight, Ali struggled at times during his 15th-round TKO of Oscar Bonavena, an unorthodox Argentinian fighter who was prepared by Hall of Fame trainer Gil Clancy. On the March 4, 1971, episode of The Dick Cavett Show, Howard Cosell, Joe Louis and Jimmy Breslin all correctly predicted that because of Ali's lengthy layoff, Frazier would prevail.

Frazier had an outstanding left hook and was a tenacious competitor who attacked the body of his opponent ferociously. Despite suffering from a serious bout of hypertension in the lead-up to the fight, he appeared to be in top form as the face-off between the two undefeated champions approached.

Prior to the fight, Mark Kram wrote in Sports Illustrated:

The thrust of this fight on the public consciousness is incalculable. It has been a ceaseless whir that seems to have grown in decibel with each new soliloquy by Ali, with each dead calm promise by Frazier. It has magnetized the imagination of ring theorists, and flushed out polemicists of every persuasion. It has cut deep into the thicket of our national attitudes, and it is a conversational imperative everywhere—from the gabble of big-city salons and factory lunch breaks rife with unreasoning labels, to ghetto saloons with their own false labels.

As Gil Clancy, who was in Frazier's corner that night, would later comment:

The electricity in the air then was just unbelievable. If they would have droppe…

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The fight was broadcast live pay-per-view on theatre television in the United States, where it set a record with 2.5 million tickets sold at closed-circuit venues, grossing $45 million. It was also shown closed-circuit during the middle of the night in London theatres, where it set a record with 90,000 tickets, grossing $750,000. Combined, the fight sold 2.59 million tickets in the United States and London, grossing $45.75 million (inflation-adjusted $300 million).

On both closed-circuit and free television, the fight was watched by a record 300 million viewers worldwide. It was watched by a record 27.5 million viewers on BBC1 in the United Kingdom, about half of the British population. It was also watched by an estimated 5.4 million viewers in Italy, and 2 million viewers in South Korea.

Ali refused to publicly admit defeat and sought to define the outcome in the public's mind as a "White Man's Decision". Frazier lost the title 22 months later, when he was knocked down six times in the first two rounds by George Foreman in their brief but devastating January 22, 1973, title bout in Kingston, Jamaica.

Ali split two bouts with Ken Norton in 1973 and was viewed by many as on a downward slide before a win in a rematch—Ali–Frazier II—in January 1974. That October, Ali shocked the world with a victory in Kinshasa, Zaire, over the heavily favored Foreman to regain the heavyweight title in The Rumble in the Jungle.

Ali later went on to defeat Frazier in their third and final bout, The Thrilla in Manila, in 1975. By the time of the rematches the social climate in America had settled down, with the Vietnam War having ended in early 1973. Many dismissed the notion that Ali was a traitor, and he was once again accepted as the heavyweight champion. People who had supported Frazier on political and racial grounds in the first bout so that they could see Ali get beat were less effusive and abandoned him after he lost his championship. Without the same social divide, with the unknown of whether Ali could ever regain enough of his former greatness to dominate post-layoff partially answered, and without the impetus of two unbeaten champions meeting one another for the first time, neither their second nor their third matchup would attain the unprecedented hype of the first.