Muhammad Ali was remembered in tributes worldwide for his iconic fight for social justice as well as his legendary boxing battles following his death on Friday at age 74.
"We lost a giant," Filipino fighter Manny Pacquiao said. "Boxing benefitted from Muhammad Ali's talents but not as much as mankind benefited from his humanity."
George Foreman, Ali's most famous knockout victim from the Rumble in the Jungle, noted Ali's other main rival, Joe Frazier, in tweeting: "Ali, Frazier and Foreman we were 1 guy. A part of me slipped away, The greatest piece."
The front page headline on Ali's hometown newspaper, the Courier-Journal of Louisville, Kentucky, simply said, "The Greatest" with a legendary 1965 photo of Ali standing over a flattened Sonny Liston.
Ali spoke out for African-American civil rights in the 1960s, carrying on his fight against injustice and sacrificing the prime years of his own career in the process.
"When people saw what he had done for what he believed in, threw away 3 1/2 years of his career and he remained steadfast, he came through all of that bigger and more important than ever before," boxing promoter Bob Arum said.
Retired NBA all-time scoring leader Kareem Abdul-Jabbar praised Ali's courage in fighting discrimination.
"At a time when blacks who spoke up about injustice were labelled uppity and often arrested, Muhammad willingly sacrificed the best years of his career to stand tall and fight for what he believed was right," said Abdul-Jabbar. "In doing so, he made all Americans, black and white, stand taller. I may be 7-feet-2 but I never felt taller than when standing in his shadow."
Ali spirit 'will never die' 
Boxing began mourning its greatest star with ultimate praise.
"We lost a legend, a hero and a great man," said Floyd Mayweather, who retired last year as an unbeaten welterweight champion. "He's one of the guys who paved the way for me to be where I'm at. Words can't explain what Muhammad Ali did for the sport."
Former world heavyweight champion Mike Tyson tweeted: "God came for his champion. So long great one. @MuhammadAli TheGreatest RIP."
Four-time heavyweight champion Evander Holyfield said he was inspired by Ali.
"It's a great loss," Holyfield said. "Someone asked me if I wanted to break his record (as a three-time champion) and I said no because that means I have to lose. But you find out you have to be stronger to get up from a loss to go on. And that's what Ali proved."
Don King, who promoted the Rumble in the Jungle, said Ali will live on forever alongside other US civil rights heroes.
"He was tremendous, not just a boxer, a great human being, an icon," King said. "Muhammad Ali's spirit, like Martin Luther King Jr., will live on. That's why Muhammad Ali will never die."
NBA commissioner Adam Silver also hailed Ali's immortality and courage.
"Muhammad Ali transcended sports with his outsized personality and dedication to civil rights and social justice," Silver said. "While we are deeply saddened by his loss, Muhammad Ali's legacy lives on in every athlete who takes a stand for what he or she believes."
'Legacy will forever endure' 
Ali won an Olympic gold medal in 1960 and lit the torch at the 1996 Olympic opening ceremony.
"The sports world has lost one of its most iconic figures," US Olympic Committee chief executive officer Scott Blackmun said. "With unparalleled grit and determination, he left a legacy that will continue to inspire."
Los Angeles 2024 Olympic bid vice chair Janet Evans, a four-time Olympic champion swimmer who handed Ali the torch in 1996, said Ali "inspired me and millions of others around the world to be the best version of ourselves. He will be sorely missed, but his legacy will forever endure."
Retired US fighter and promoter Oscar de la Hoya said Ali "exemplified courage. He never took the easy route, something to be admired in and outside of the ring."
Today's top boxers paid triubute to Ali, with Saul "Canelo" Alvarez tweeting: "My idol has left us. I will always remember you as the best and will follow ur example. Your legend will live forever" and Gennady Golovkin tweeting: "The Greatest. In boxing and in life, an inspiration to mankind."