Obama described Ali as "a man who fought for what was right. A man who fought for us. He stood with King and Mandela; stood up when it was hard; spoke out when others wouldn’t." But, Obama, said, "For all his magic in the ring, he could be careless with his words, and full of contradictions as his faith evolved. But his wonderful, infectious, even innocent spirit ultimately won him more fans than foes."
Former president Bill Clinton released a lengthy statement about three hours after the passing of Ali was announced, on behalf of himself and his Democratic presidential hopeful wife Hillary Clinton.
"Hillary and I are saddened by the passing of Muhammad Ali," the statement read. "From the day he claimed the Olympic gold medal in 1960, boxing fans across the world knew they were seeing a blend of beauty and grace, speed and strength that may never be matched again."
The Bernie Sanders campaign followed, saying, "Muhammad Ali was the greatest, not only an extraordinary athlete but a man of great courage and humanity."
Former president George W. Bush released a statement on Ali's passing, remembering when he awarded the legendary boxer with the Presidential Medal of Freedom in 2005, the highest civilian award in the United States.
"Muhammad Ali was an iconic and historic figure who thrilled, entertained, influenced, and inspired millions. Americans will always be proud to have been in his corner and called him one of our own," the statement read. "Laura and I send our heartfelt condolences to Muhammad Ali's family and friends."
Tyson wrote, "God came for his champion. So long great one."
Mayweather wrote on Instagram, "Today my heart goes out to a pioneer, a true legend, and a hero by all means!"
De La Hoya captioned a photo of himself with Ali, "RIP @muhammadali, a legend who transcended sport and was a true champion for all. #thegreatest #MuhammadAli."
Jones tweeted, "My heart is deeply saddened yet both appreciative and relieved that the greatest is now resting in the greatest place," and posted a photo of Ali on his Facebook page, as well.
In a telephone interview with BBC Radio 4 today, Foreman said he will never forget the infamous "Rumble in the Jungle" fight on a humid evening in Kinshasha, capital of the former Zaire, in 1974. Ali fought then-champion Foreman and won back the title in eight rounds.
"I'll remember that with the most fond of memories," Foreman said on BBC Radio 4. "What a night! I was in the ring with one of the greatest human beings."
Foreman said calling Ali the world's greatest boxer is "an insult."
"The greatest boxer? Give that to some boxer. Muhammad Ali was one of the greatest human beings I ever met in my life," Foreman said on BBC Radio 4 today. “A piece of me died when he passed away, and I call it the greatest piece.”
Public figures from the worlds of media, business, and Hollywood also joined in the remembrance of Ali.
Justin Bieber posted a photo of Ali on Instagram, writing, "This is the ALI we should all remember! The fun loving man who was fully himself!! RIP CHAMP!!!"
Sean "Diddy" Combs posted on Instagram a photo of himself, his son and Ali at a basketball game, writing "Thank you for always showing me and my family love. He was so kind to everyone he met! I want my son @princejdc to always cherish this moment. #RIPALI we miss you. We love you. You have changed the world. And taught us all something REST IN PEACE GREAT ONE"
Rapper and actor Snoop Dogg posted a series of tweets with photos, including this one with the two of them.
The first of the Kardashian-Jenner sisters to post a tribute to Ali was Kylie Jenner, who posted a black-and-white photo of Ali.
Twitter co-founder Jack Dorsey tweeted a black-and-white photo of Ali in the ring, writing, "Service to others is the rent you pay for your room here on earth."
The Council on American-Islamic Relations (CAIR), the nation's largest Muslim civil liberties and advocacy organization, called Ali "a true Muslim" and "a champion for peace and justice."
"Muhammad Ali, a man who stood by his principles despite criticism and hardship, exemplified a true patriot and a true Muslim," CAIR national board chair Roula Allouch said in an online statement Saturday. "His strength, courage and love of humanity has been, and will continue to be, an inspiration to people of all faiths and backgrounds in America and worldwide."
"Ali's legacy as a champion for peace and justice will motivate generations to come to make our world a better place," CAIR national executive director Nihad Awad said in the statement. "To God we belong and to Him we return."
ABC News' Alexandra Faul and Christopher Donato contributed to this report.