Muhammad Ali – the charismatic, self-proclaimed King of the World, who persevered to win the heavyweight boxing title three different times – has died at the age of 74, according to reports.
A family spokesperson confirmed to NBC News that Ali died Friday at the Phoenix-area hospital, that he had spent the past few days being treated for respiratory complications.
The death comes just days after the boxing legend was hospitalized with a respiratory issue. His rep told PEOPLE the that Ali was in "fair condition" and was expected to have a "brief" stay at the hospital.
The outspoken boxing great had long been battling Parkinson's disease. He was first diagnosed in 1984, three years after his retirement from boxing.
In March, Ali's daughter, Laila Ali, told PEOPLE that she was amazed by her father's strength in the midst of his failing health.
"He's such a fighter, still, when at times he seems weak and not able to handle it," she said. "He comes through stronger than ever. He's still fighting regardless and I love my dad for that."
Ali's friend Davis Miller echoed his daughter's statements, telling PEOPLE in March that the champion "fights every day, all day long."
"There's a magic about Muhammad Ali – everything from his elegance in the ring to his sense of humor," Miller said.
What Ali never aimed to be was modest.
Declaring himself to be "the greatest" and "the prettiest" of all time, Ali introduced into the riotous turmoil of the '60s the revolutionary notion that black was both powerful and beautiful.
As the 25-year-old reigning world champion in 1964, he refused to be drafted into the U.S. Army and instead changed his name from Cassius Clay and declared himself to be an Islamic minister intent on helping his people.
"I had to prove you could be a new kind of black man," he told his biographer David Remnick, while to the media and the boxing establishment at large he announced, "I don't have to be what you want me to be."
A Champ at 12
The son of Cassius Clay Sr., a sign painter, and Odessa, a housekeeper, Cassius Marcellus Clay Jr. was born Jan. 17, 1942, in Louisville, Kentucky. He started his boxing career as an 89-lb. 12-year-old, winning a three-round, three-minute fight against someone of equal weight.
By the time he was 18, the 6' 3", 210-lb. slugger had compiled an extraordinary record of 100 wins and eight losses, two national Golden Gloves championships and two national Amateur Athletic Union titles.
That same year Clay won the light heavyweight championship at the 1960 Rome Olympics. He cherished his medal, wearing it day and night for weeks.
Thereafter, he turned professional, and on Feb. 25, 1964, wearing a white robe with "The Lip" embroidered on the back, he entered the ring to fight the reigning champion, Sonny Liston, for the heavyweight title.
Despite his boisterous claims that he would "put that ugly bear on the floor … and build myself a pretty home and use him as a bearskin rug," nearly all of the sportswriters covering the event predicted Liston would win."
That didn't happen. Just as he had claimed he would, Clay defeated Liston to become the heavyweight champion of the world.
Clay, now Muhammad Ali, was undefeated after 29 professional fights and had defended his title seven times when, in 1967, he was drafted to serve in the Vietnam war. Claiming exemption as a minister of the religion of Islam, he refused to be inducted.
Convicted of draft evasion, he remained free pending an appeal, but by the time the Supreme Court reversed the conviction four years later, Ali had been stripped of his title and had lost the prime years of his boxing career, as well as millions of dollars in potential fees.
Ali regained his heavyweight title in 1974, defeating George Foreman in the dramatic "Rumble in the Jungle" in Zaire, Africa. He fought 22 fights after Zaire, including the "Thrilla in Manila" in 1975 (when he defeated Joe Frazier in one of the epic fights in boxing history) and two championship bouts against Leon Spinks, in which he first lost his title and then regained it seven months later.
Retired in 1981
Already feeling the paralyzing effects of Parkinson's, he retired in 1981, five weeks before his 40th birthday, with a record of 56 wins and 5 losses, with 37 knockouts.
Named a Messenger of Peace by the United Nations in 1998, "Over the years Mr. Ali has been a relentless advocate for people in need and a significant humanitarian actor in the developing world, supporting relief and development initiatives and hand-delivering food and medical supplies to hospitals, street children and orphanages in Africa and Asia," the organization said.
As Ali told PEOPLE, "One day you wake up and it's Judgment Day. So you do good deeds."