Ali died on Friday after a three-decade long battle with Parkinson's disease, but his place as one of the greatest sportsmen of all time will remain.
We take a look at some of Ali's most high-profile celebrators here:
One of the few athletes to dominate a sport as Ali did, Tiger Woods wrote: "You'll always be The Greatest for more than just what you did in the ring. A champion to so many people in so many ways."
David Beckham, one of the few sporting stars to transcend their arena as much as "the biggest and the best" Ali, shared an image of a meeting between them.
Three-time Formula One world champion Lewis Hamilton added well-wishes to Ali's family on Instagram.
"My hero since childhood," Indian cricketing royalty Sachin Tendulkar tweeted. "I always had a wish to meet you some day but now it will never happen."
From one champ to another. Eight-weight world champion Manny Pacquiao said: "Boxing benefitted from Muhammad Ali's talents but not nearly as much as mankind benefitted from his humanity."
The only sportsman to hold a candle to Ali's popularity at the peak of his powers was Brazilian soccer legend Pele. The World Cup-winning striker admitting he was overwhelmed with grief after his friend's passing.
Women's tennis pioneer Billie Jean King paid tribute to Ali's impact made out of the ring, hailing "a man who was not afraid to take a stand and who was committed to being his authentic self".
A heavyweight world champion for almost a decade unbeaten, Wladimir Klitschko remembered "a man of character, faith, dignity and professionalism."
Ali once claimed: "I'm so fast that last night I turned off the light switch in my hotel room and got into bed before the room was dark." Perhaps the only man who could match the champ's speed is fastest man on the planet Usain Bolt, who selected another of Ali's famous quotes to sum up his legacy.
"He who is not courageous enough will achieve nothing in life."