Boxing legend Muhammad Ali dies aged 74

Ali is widely considered one of the greatest ever heavyweight boxers Credit: PA

Boxing legend Muhammad Ali has died at the age of 74, a family spokesman confirmed.

The three-time world heavyweight champion was being treated in a Phoneix-area hospital for a respiratory condition.

A statement from the Bob Gunnell, the family, spokesman said the Ali family "would like to thank everyone for their thoughts, prayers and support" and asked for privacy.

Earlier, the website Radar Online reported that members of Ali's family had gathered at his hospital bedside.

His daughter, Laila Ali, also a former boxer, posted a photo with her father on Facebook, and thanked fans for their support.

She wrote: "Thank for all the love and well wishes. I feel your love and appreciate it!"

Mike Tyson, George Foreman, and Lennox Lewis were among many well-known figures in the boxing world who paid tribute to the charismatic former champion.

The man many hailed 'the greatest'

Born Cassius Marcellus Clay, Ali is widely considered one of the greatest heavyweight boxers in the history of the sport.

He liked to say he was more famous than the Pope and the US president rolled into one, and at the height of his career that was probably true.

But he became much more than simply a colorful and interesting athlete - he was outspoken against racism in the 1960s, as well as the Vietnam War.

Muhammad Ali takes part in an anti-war demonstration in 1967. Credit: PA

Ali began training at the age of 12, and just a decade later won the world heavyweight championship in 1964 from Sonny Liston.

He famously won the title again in 1974 against George Foreman in "The Rumble In The Jungle", and in 1978 against his rival Joe Frazier.

A poster for the Rumble in the Jungle

Ali's rivalry with Frazier is the stuff of legend, and their final boxing match in 1975, "Thrilla in Manila" is consistently ranked as one of the best fights in boxing history.

'Thrilla in Manila': Muhammad Ali v Joe Frazier in 1975. Credit: PA

He was diagnosed with Parkinson's in 1984, thought to be a result of head trauma from his boxing days.

A funeral service is planned in his hometown of Louisville, Kentucky.