The Ali-Frazier 1971 ‘Fight of the Century’ provided cover for a mission to expose the FBI. March 7, 2021. Joe Frazier stands over Muhammad Ali in the 15th round of their bout March 8, 1971.

As LIFE observed in its March 5, 1971 issue: “[Ali] and Frazier are both going to get $2.5 million the morning after the fight whether anybody comes or not. A flat $2.5 million. Guaranteed.

Muhammad Ali looks up toward Joe Frazier after getting knocked down during their 1971 title fight at Madison Square Garden in New York. (Associated Press) By 1971, Tim Ryan had advanced past the ...

Joe Frazier, left, hits Muhammad Ali during the 15th round of their heavyweight title fight at Madison Square Garden on March 8, 1971. Credit: AP/Anonymous ...

Joe Frazier, the heavyweight champion of the world, spent the morning of March 8, 1971, in a New York hotel, but it wasn’t the one he had checked into after making the short drive from his home ...

Muhammad Ali vs. Joe Frazier was billed as the 'Fight of the Century,' held on March 8, 1971, at Madison Square Garden in New York City. The match lasted 15 rounds with the judges declaring ...

Down goes Ali: In the "Fight of the Century," on March 8, 1971, in Madison Square Garden, heavyweight champion Joe Frazier put Muhammad Ali on the canvas with a hard left hook. Frazier died Monday.

Muhammad Ali in red trunks, and Joe Frazier in green trunks, during round 5 or 6 of their bout at Madison Square Garden on March 8, 1971. “Guys can get dejected,” he continued.

In this March 8, 1971, file photo, boxer Joe Frazier, left, knocks downs Muhammad Ali during the 15th round of their heavyweight title fight at New York's Madison Square Garden. Anonymous AP ...

Joe Frazier hits Muhammad Ali with a left during the 15th round of their heavyweight title fight at New York’s Madison Square Garden in this March 8, 1971, file photo. Frazier was a relentless ...

Joe Frazier took home the win in the fight against Muhammad Ali, held at Madison Square Garden in New York City on March 8, 1971 ...

Frazier stands above Ali during the 15th round of their first fight, also held at Madison Square Garden in March 1971. AP. The Garden erupted. Frazier drew the unanimous decision — and a three ...