Tributes have poured in from across the world for boxing legend Muhammad Ali, who has died at the age of 74.
"Muhammad Ali shook up the world. And the world is better for it," said US President Barack Obama.
The three-time world heavyweight champion - one of the world's greatest sporting figures - died on Friday night at a hospital in Phoenix, Arizona.
He died from "septic shock due to unspecified natural causes", said a spokesman for the Ali family.
The boxer had been suffering from a respiratory illness, a condition that was complicated by Parkinson's disease.
"I am happy my father no longer struggles. He is in a better place. God is the greatest," his daughter Maryum said on Saturday.
Ali's body is being returned in the next two days to his hometown of Louisville, Kentucky, where his funeral is scheduled for Friday afternoon at the KFC Yum! Center.
The celebration of his life will feature a funeral procession through the town and public celebration. The boxer will be buried in a private service at the city's Cave Hill Cemetery.
The service will be presided over by an imam and feature eulogies by former President Bill Clinton, sports journalist Bryant Gumber and actor Billy Crystal.
Many residents of Louisville, Kentucky, woke up on this hazy Saturday morning to the news: Muhammad Ali is dead.
The news of his death is on every local television station, and the front page of the local newspaper reads simply "The Greatest" over the iconic image of Ali standing victorious over Sonny Liston in 1965.
Flags at Louisville's city hall will fly at half mast today and the mayor will deliver a memorial service there.
Almost everyone has a personal story about Ali, whether it's a favourite fight, a glance through a car window, or a trip to his boyhood home, which opened as a museum only last week, the interior recreated as if Ali were still living there as a precocious 12-year-old boy in the 1950s.
Ali was as much a campaigner for black equality as he was a champion in the ring, where he won 56 of his 61 fights.
Asked how he would like to be remembered, he once said: "As a man who never sold out his people. But if that's too much, then just a good boxer.
"I won't even mind if you don't mention how pretty I was."
But he was once a polarising figure in the US. At a time of racial segregation in the 1960s he joined the separatist black sect, The Nation of Islam, which rejected the inclusive approach of civil rights leaders such as Martin Luther King.
George Foreman, who lost his world title to Ali in the famous "Rumble in the Jungle" fight in Kinshasa in 1974, called him one of the greatest human beings he had ever met.
"To put him as a boxer is an injustice," said Foreman.
American civil rights campaigner Jesse Jackson said Ali had been willing to sacrifice the crown and money for his principles when in 1967 he refused to serve in the Vietnam war.
That decision was widely criticised by the boxer's fellow Americans. He was stripped of his title and had to put his fighting career on hold for three years.
UK Prime Minister David Cameron said: "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."
UN Secretary-General Ban Ki-moon said Ali had "fought for a better world and used his platform to help lift up humanity".
Heavyweight champ at 22
Born Cassius Marcellus Clay, Ali shot to fame by winning light-heavyweight gold at the 1960 Rome Olympics.
Known as "The Greatest" - a nickname characteristically coined by the boxer himself - the American beat Sonny Liston in 1964 to win his first world title and became the first boxer to capture a world heavyweight title on three separate occasions.
Noted for his pre- and post-fight talk and bold fight predictions as much as his skills inside the ring, he retired in 1981 having won 56 of his 61 fights - 37 by knockout - and was later crowned "Sports Personality of the Century" by the BBC.
Ali turned professional immediately after the Rome Olympics and rose through the heavyweight ranks, delighting crowds with his showboating, shuffling feet and lightning reflexes.
British champion Henry Cooper came close to stopping Clay, as he was still known, when they met in a non-title bout in London in 1963.
Cooper floored the American with a left hook, but Clay picked himself up off the canvas and won the fight in the next round when a severe cut around Cooper's left eye forced the Englishman to retire.
In February the following year, Clay stunned the boxing world by winning his first world heavyweight title at the age of 22.
He predicted he would beat Liston, who had never lost, but few believed he could do it.
Yet, after six stunning rounds, Liston quit on his stool, unable to cope with his brash, young opponent.
At the time of his first fight with Liston, Clay was already involved with the Nation of Islam, a religious movement whose stated goals were to improve the spiritual, mental, social, and economic condition of African Americans in the US.
But in contrast to the inclusive approach favoured by civil rights leaders like Dr Martin Luther King, the Nation of Islam called for separate black development and was treated by suspicion by the American public.
Ali eventually converted to Islam, ditching what he perceived was his "slave name" and becoming Cassius X and then Muhammad Ali.
After his conviction for refusing the draft was overturned in 1971, he returned to the ring and fought in three of the most iconic contests in boxing history, helping restore his reputation with the public.
He was handed his first professional defeat by Joe Frazier in the "Fight of the Century" in New York on 8 March 1971, only to regain his title with an eighth-round knockout of George Foreman in the "Rumble in the Jungle" in Kinshasa, Zaire (now Democratic Republic of Congo) on 30 October 1974.
Ali fought Frazier for a third and final time in the Philippines on 1 October 1975, coming out on top in the "Thrilla in Manila" when Frazier failed to emerge for the 15th and final round.
Six defences of his title followed before Ali lost on points to Leon Spinks in February 1978, although he regained the world title by the end of the year, avenging his defeat at the hands of the 1976 Olympic light-heavyweight champion.
Ali's career ended with one-sided defeats by Larry Holmes in 1980 and Trevor Berbick in 1981, many thinking he should have retired long before.
He fought a total of 61 times as a professional, losing five times and winning 37 bouts by knockout.
Soon after retiring, rumours began to circulate about the state of Ali's health. His speech had become slurred, he shuffled and he was often drowsy.
Parkinson's Syndrome was eventually diagnosed but Ali continued to make public appearances, receiving warm welcomes wherever he travelled.
He lit the Olympic cauldron at the 1996 Games in Atlanta and carried the Olympic flag at the opening ceremony for the 2012 Games in London.