Tributes have flooded in from the sports world and beyond for Muhammad Ali.
Former heavyweight boxing champion Evander Holyfield told MSNBC: "I'm glad to have known Ali because when I was a kid, at eight years old, I was told I would be like Ali.
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"To take it upon yourself and say; 'I'm the greatest', you put yourself in a position for people to take pot shots at you. This is what Ali did. It's amazing him becoming three-time heavyweight champion of the world. At that time people thought, 'Who could beat three?
"You have to be stronger to get up from a loss to go on and that's what Ali proved to be."
Former England footballer Gary Lineker tweeted: "The greatest has fought his final round. Muhammad Ali was the most magnificent athlete who transcended his sport."
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Argentinian boxer Marcos Maidana, a two-weight former world champion, tweeted: "Muhammad Ali the all-time greatest has left us. Thanks for everything. Go with God."
Musician Wyclef Jean wrote: "I am the greatest, I said that even before I knew I was. Rest in peace to the greatest @MuhammadAli #MuhammedAli we lost another legend."
British boxer Amir Khan tweeted: "Our Prayers and thoughts are with @MuhammadAli and his family #AliBomaye."
Former world champion and promoter Oscar De La Hoya wrote on Twitter: "RIP @MuhammadAli, a legend who transcended sport and was a true champion for all. #thegreatest #MuhammadAli."
Golden State Warrior Harrison Barnes added: "The greatest may be gone from public life but his spirit should live forever in our social consciousness............RIP Muhammad Ali."
Brazil midfielder Kaka on Twitter: "Rest in peace @MuhammadAli #rip."
Five-time NBA champion Tony Parker wrote: "RIP Muhammad Ali ! All my prayers and thoughts to his family. #TheGreatest."
Former heavyweight champion of the world Mike Tyson paid his tribute on Twitter: "God came for his champion. So long great one. @MuhammadAli #TheGreatest #RIP."
Rugby league and NFL player Jarryd Hayne said: "Rest In Peace Muhammad Ali. Inspiration in and out of the ring. Loved his character/personality #peopleschamp #goat."
Current middleweight champion Gennady Golovkin said: "The Greatest. In boxing and in life, an inspiration to mankind."
Current heavyweight champion Deontay Wilder said: "RIP @MuhammadAli, a legend who transcended sport and was a true champion for all. #thegreatest #MuhammadAli."
Manny Pacquiao, the former world champion and current politician, said in a statement: " We lost a giant today. Boxing benefited from Muhammad Ali's many talents but not nearly as much as mankind benefited from his humanity."
Former British heavweight champion, Frank Bruno said on Twitter: "Inspiration, Mentor, my Friend, an Earthly God of humanity, Simply."
Current promoter Eddie Hearn, who looks after current world champion Anthony Joshua, said: " Waking to the sad news that 'The Greatest' has passed. Rest in peace Muhammad Ali you shook up the World."
Prime Minister David Cameron wrote: " Muhammad Ali was not just a champion in the ring - he was a champion of civil rights, and a role model for so many people."
Lord Sugar said: "Muhammad Ali he was the greatest, not just a great boxer but he fought for racial equality. Sad Loss to the world R.I.P."
Singer Jermaine Jackson added: " As boys, we huddled around the radio as Muhammad Ali floored Sonny Liston. In 1975, he walked into, and blessed, our lives..."
Former F1 world champion Jenson Button said: " #MuhammadAli #cassiusclay "If you even dream of beating me you'd better wake up and apologize" #restinpower."
Joshua tweeted a photograph of himself and Ali wearing black suit and sunglasses, and captioned it with: "You've inspired the next generation in many different ways! Legacy lives on."