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.
“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.”
Leeds-born Nicola Adams, the world’s first female boxing champion, added: “Prayers go out to boxing’s greatest of all time and an inspiration to me and so many people.”
Yorkshireman Richard Dunn, who lost to Ali in Munich when challenging for his WBA and WBC titles in May 1976, said: “I think his legacy will last forever.
“When we’ve long gone they’ll still be talking about him and it’ll be worthwhile as well. He was such a fantastic champion.
“[If young boxers] watch his fights and see what a great athlete he was and they want to be the same then it’s there for them. He’s a good example. He was a hell of a fighter.”
Yorkshire broadcaster Sir Michael Parkinson, who had a series of famously combative interviews with the boxer, said: “He was not a man without flaws. You have to consider those. But if you wanted to concentrate on what was attractive about him I could talk forever.”
He added: “I could not believe how beautiful he was. He was an extraordinary looking man. He was graceful and all those things and, of course, he was as funny as hell.”
Prime Minister David Cameron tweeted: “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.”
Former England footballer Gary Lineker tweeted: “The greatest has fought his final round. Muhammad Ali was the most magnificent athlete who transcended his sport.”
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.”
British boxer Amir Khan tweeted: “Our Prayers and thoughts are with @MuhammadAli and his family #AliBomaye.”
Former heavyweight champion Mike Tyson tweeted: “God came for his champion. So long great one. @MuhammadAli #TheGreatest #RIP.”
Joe Calzaghe, the British former two-weight world champion, told the BBC: “People loved him, he was someone completely different, backed it up in the ring and everybody wanted to tune in and watch him fight.
“He was a superstar. There’ll never be another Muhammad Ali, in a thousand years’ time people will look back and say he was the greatest.
“He was my inspiration, I tried to copy some of his moves and it is a truly sad day. But I’m proud that my sport of boxing has probably the greatest all-round sportsman of all time.”
Former Pakistani cricketer Imran Khan called Ali the “greatest sportsman of all times”, saying: “What set Ali apart from other great sportsmen and what I most admired him for was his refusal to compromise on his belief and value system.
“Ali was stripped of his world heavyweight title and lost millions in earnings because he refused to fight in Vietnam but he stood resolute.”
David Beckham posted a photograph of himself meeting Ali and called him “the greatest there will ever be ... the biggest and the best”.
He also posted a quote from Ali on Instagram: “Impossible is just a big word thrown around by small men who find it easier to live in the world they’ve been given than to explore the power they have to change it.
“Impossible is not a fact. It’s an opinion. Impossible is not a declaration. It’s a dare. Impossible is potential. Impossible is temporary. Impossible is nothing.”
Former heavyweight world champion Lennox Lewis said Ali was “a giant among men”, adding: “Ali displayed a greatness in talent, courage and conviction that most of us will ever be able to truly comprehend.”
And Frank Bruno added: “Inspiration, mentor, my friend, an Earthly god of humanity, simply the greatest.”
Rev Jesse Jackson told BBC Radio 4’s Today programme: “He became a champion inside the ring and a hero outside. Champion because he won the boxing matches, hero because he stood up against the war in Vietnam.”
WBC world champion Tony Bellew called Ali “the greatest sporting icon of all time” and said he “transcended boxing an(d) put our sport on the map”.
IBF super-middleweight champion James DeGale added: “A very sad day for my sport. There are few real heroes left in this world. Today we lost ‘The Greatest of All Time’.”
Former England rugby star Matt Dawson said: “My sporting hero leaving us all. I met you in 1999 and will never forget the life in your eyes.”
Boxing champion Floyd Mayweather Jr told Fox News: “There will never be another Muhammad Ali. The black community all around the world, black people all around the world, needed him. He was the voice for us. He’s the voice for me to be where I’m at today.
“I just want to thank Muhammad Ali and his family for being such strong people. You will always be missed. My prayers go out to Ali and his family.”
George Foreman, Ali’s friend and rival from the famous “Rumble in the Jungle” fight, told the BBC: “We were like one guy – part of me is gone.”
“Muhammad Ali was one of the greatest human beings I have ever met. No doubt he was one of the best people to have lived in this day and age.
“To put him as a boxer is an injustice.”
He also spoke of Ali’s love for the UK and the way he was treated in the country.
“He loved London. If he had been born and raised in London he never would have changed his name,” he said.
Ali’s former promoter Don King told CNN: “He’s always been right there, Johnny on the spot, anything he could do for the benefit of mankind.
“Let us celebrate his life. This is not a time to mourn. This is a time to try to emanate the job he was doing and the burden he leaves behind for us to carry on, to remember that the people are the most important.”