"The Greatest" died aged 74 after respiratory problems compounded by his Parkinson's Disease
Muhammad Ali's daughter has said his family is "so happy daddy is free now" in a moving tribute, after the boxing legend passed away at the age of 74.
Hana Ali said their hearts "are literally hurting" as she thanked friends and fans for their love and support.
She said he was surrounded by relatives who embraced him and prayed during his final moments.
She said his heart had kept beating for 30 minutes after his organs had failed, describing his passing as "a true testament to the strength of his spirit and will."
The three-time world heavyweight champion was diagnosed with Parkinson's disease in 1984 - three years after he retired from the sport.
Ali had been admitted to hospital in the days before his death suffering from respiratory issues.
His brother Rahman Ali described him as a "kind, loving, considerate, wonderful" man.
He said: "He loved people. Black, white - he loved all people."
Reports had suggested his breathing problems had been complicated by the neurological disorder, which had long impaired his speech.
Ali's funeral will take place in his hometown of Louisville, Kentucky, on Friday, a spokesman said.
Flowers, cards, and signs have been piling up outside his childhood home, with cars lining both sides of the street for blocks.
Boxing stars past and present, including Mike Tyson, George Foreman and Amir Khan, are among those who have paid tribute to Ali, while political leaders including Barack Obama have also expressed sadness at the news.
Boxing manager Frank Warren told Sky News that "the world lost an iconic figure", describing Ali as "one of the greatest of all time".
"(He) became bigger than sport", Warren said, adding: "Muhammad Ali probably paved the way for Barack Obama becoming President of the United States.
"He changed the whole concept of being black in America."
US civil rights campaigner Reverend Al Sharpton said: "The legacy of Muhammad Ali is not just that he just floated in the ring, but that he stood up outside the ring.
"He was a champion out of the ring, and in the ring ... he was the greatest of all time in his sacrifice, in his dedication and in his commitment."
Chat show host Michael Parkinson, who interviewed Ali several times, said he was "the most extraordinary and unique" individual he had ever interviewed.
He said: "There was an autumnal feel to him, that's the only way I can describe it. We talked about the possibility of boxers being mentally damaged.
"I looked at him the last time and thought, I will not see you again.
"You felt like you were interviewing a Martian or someone from out of space.
"The walls of conversation did not apply to him. When he took off on one of his flights of fancy, you just enjoyed the ride."