Frazier, who had been suffering from liver cancer, died overnight at the age of 67, his family confirmed in a statement.
This morning tributes poured in from throughout the world of boxing and beyond.
But it is his fights with Ali for which Frazier is best remembered. Frazier beat Ali on points in the so-called “Fight of the Century” in 1971, but lost in two further meetings including the epic “Thrilla in Manila” in 1975.
Today Ali said: “The world has lost a great champion. I will always remember Joe with respect and admiration.
“My sympathy goes out to his family and loved ones.”
The pair had an at-times fraught relationship, dating back to taunts Ali directed at his rival in the build-up to their famous trilogy of fights.
But they were reported to have been on better terms in recent years.
Boxing stars of a more recent era took to Twitter to share their thoughts, with Floyd Mayweather writing: “RIP Smokin Joe.” The fighter known as ‘Money’ continued: “TheMoneyTeam will pay for his Funeral services.”
Oscar De La Hoya wrote: “I will miss you my friend.”