Muhammad Ali, the record-setting world heavyweight champion whose personality transcended sports, has died at the age of 74.

Ali's death was confirmed in a statement issued by family spokesman Bob Gunnell late on Friday evening, a day after he was admitted to a Phoenix-area hospital with a respiratory ailment.

The cause of death or the name of the hospital where he died were not immediately disclosed.

READ MORE: Muhammad Ali, a life in quotes

Ali had long suffered from Parkinson's disease, which impaired his speech and made the once-graceful athlete almost a prisoner in his own body.

Nevertheless, Ali's youthful proclamation of himself as "the Greatest" rang true until the end for the millions of people worldwide who admired him for his courage, both inside and outside the ring.

Muhammad Ali 1942-2016 Muhammad Ali was born Cassius Marcellus Clay Jr on January 17, 1942, in Louisville, Kentucky Aged 22, he took on heavyweight champion Sonny Liston in Miami. He won and proclaimed to the world: "I am the greatest!" Ali was the first man to win heavyweight titles three times Ali attended his first Nation of Islam meeting in 1959 and converted to Sunni Islam in 1975 In 1967, he famously refused to fight in Vietnam, citing religious reasons Married four times, he had seven daughters and two sons He was diagnosed with Parkinson's disease in 1984 at the age of 43 Ali died late on June 3, 2016, in a hospital in Arizona after being admitted with respiratory problems

"A part of me slipped away, the greatest piece," George Foreman, a former heavyweight boxer and one of Ali's most formidable opponents in the ring, said on Twitter after the news of Ali's death.

Roy Jones Jr, a former champion boxer who grew up during Ali's prime, also said on Twitter: "My heart is deeply saddened yet both appreciative and relieved that the greatest is now resting in the greatest place."

Few could argue with his athletic prowess at his peak in the 1960s.

With his dancing feet and quick fists, he could, as he put it, "float like a butterfly and sting like a bee".

He finished with a record of 56-5 with 37 knockouts and was the first man to win heavyweight titles three times.

However, Ali became much more than a colourful and interesting athlete.

He spoke boldly against racism in the 1960s, as well as the Vietnam War.

During and after his championship reign, Ali met scores of world leaders, travelled to promote Islam and for a time he was considered the most recognisable person on earth, known even in remote villages far from the US. Al Jazeera's Rob Reynolds, reporting from Los Angeles, said: "Ali was a product of his time, of the civil rights movement, of the Black Power movement. Coming of age, he was the symbol of the emergence of that way of thinking in the US. READ MORE: Muhammad Ali, a life in pictures

What is Parkinson's disease? - Parkinson's disease is a movement disorder that is chronic and progressive, and its cause is unknown - It results from loss of certain brain cells and its symptoms are ongoing ones that worsen over time - The disorder is marked by trembling in legs, arms and face as well as impaired balance and coordination - There is no known cure to the disorder, but there are treatment options to manage its symptoms Source: Parkinson's Disease Foundation

"Things such as his conversion to Islam and his opposition to the Vietnam War, made him more than an athlete and a sports superstar. These made him more of a cultural figure."

Ali once estimated that he had made $57m in his professional career, but the effect of the punches lingered long after most of the money was gone.

Ali's diagnosis of Parkinson's disease came about three years after he retired from boxing in 1981.

His influence extended far beyond boxing. He became the unofficial spokesman for millions of blacks and oppressed people around the world because of his refusal to compromise his opinions and the fact that he stood up to white authorities.

"I can't imagine a world without Mohammad Ali," Lou Eisen, a boxing writer and historian, told Al Jazeera from Toronto, Canada.

"He has been such a towering figure. Not only in sports, but also culturally, politically and socially. He loved everyone and everyone who met him loved him.

Ralph Ali, Frazier & Foreman we were 1 guy. A part of me slipped away, "The greatest piece" https://t.co/xVKOc9qtub — George Foreman (@GeorgeForeman) June 4, 2016

"There is no bitterness in the man. He was not bitter towards the government or the boxing association, which did a lot of illegal things to him.

"He did not let the bitterness get to him."

In a realm where athletes often battle inarticulateness as well as their opponents, Ali was known as the Louisville Lip and loved to talk, especially about himself.

"Humble people, I've found, don't get very far," he once told a reporter. Once asked about his preferred legacy, Ali said: "I would like to be remembered as a man who won the heavyweight title three times, who was humorous and who treated everyone right. "As a man who never looked down on those who looked up to him ... who stood up for his beliefs ... who tried to unite all humankind through faith and love.

"And if all that's too much, then I guess I'd settle for being remembered only as a great boxer who became a leader and a champion of his people. And I wouldn't even mind if folks forgot how pretty I was."

READ MORE: Memories of 'Thrilla in Manila'

Ali was born in Louisville, Kentucky, on January 17, 1942, as Cassius Marcellus Clay Jr, a name shared with a 19th century slavery abolitionist. He changed his name after his conversion to Islam.

Ali was survived by his wife, the former Lonnie Williams, who knew him when she was a child in Louisville, along with his nine children.