Legendary heavyweight champion and social icon Muhammad Ali has died, a family spokesman said late Friday in a statement.

He was 74.

Ali had been hospitalized in the Phoenix area this week with respiratory issues. The Paradise Valley Police Department told ABC News that an emergency medical services call was made from Ali's address in the Phoenix area on Tuesday, and the Phoenix Fire Department confirmed it responded to a call for mutual aid for a 74-year-old male with respiratory issues at that time.

Retired from boxing since 1981, Ali had battled Parkinson's disease for decades. He had been hospitalized a few other times in recent years, including in early 2015, due to a severe urinary tract infection initially diagnosed as pneumonia.

Ali had looked increasingly frail in public appearances, the last coming April 9 when he wore sunglasses and was hunched over at the annual Celebrity Fight Night dinner in Phoenix, which raises funds for treatment of Parkinson's. He had been living quietly in the Phoenix area with his fourth wife, Lonnie, whom he married in 1986.

Ali's funeral will take place in his hometown of Louisville, spokesman Bob Gunnell said in the statement. No further details were expected to be released until Saturday morning.

Ali's death reaches far beyond the sport of boxing.

Ali was one of the world's most recognized people for his actions in and out of the ring. His stance on the military draft and conversion to Islam polarized America mainly along racial lines. Yet later he unified people with his messages of freedom, peace and equality.

Reaction from the news was immediate.

"Words can't explain what Muhammad Ali (has) done for the sport of boxing," Floyd Mayweather told ESPN. "He's one of the guys that paved the way for me to be where I am today. We lost a legend, a hero and a great man."

Said Cleveland Cavaliers star LeBron James: "The reason why he's the GOAT [Greatest of All Time] is not because of what he did in the ring, which was unbelievable. It's what he did outside of the ring, what he believed in, what he stood for — along with Jim Brown and Oscar Robertson, Lew Alcindor, obviously who became Kareem [Abdul-Jabbar], Bill Russell, Jackie Robinson. Those guys stood for something. He's part of the reason why African-Americans today can do what we do in the sports world. We're free. They allow us to have access to anything we want. It's because of what they stood for, and Muhammad Ali was definitely the pioneer for that."

Added Bob Arum, who promoted 27 Ali fights: "A true great has left us. Muhammad Ali transformed this country and impacted the world with his spirit. His legacy will be part of our history for all time."

Ali was born on Jan. 17, 1942, and was named Cassius Marcellus Clay Junior. His father, Cassius Marcellus Clay Senior, was named after a 19th-century white abolitionist. Clay Sr. made a living painting billboards and signs. His mother, Odessa Grady Clay, worked as a domestic servant.

At age 12 he took up boxing under the tutelage of Joe Martin, a Louisville policeman who became Clay's trainer for his amateur career. During that time Clay won two national Golden Gloves titles and one AAU championship. After graduating from high school he won the light heavyweight gold medal at the 1960 Olympics in Rome.

After the Olympics, Clay turned professional. Fighting as a heavyweight he won his first 19 bouts and had Angelo Dundee as his trainer. Clay exhibited quick hands, nimble footwork and an active mouth. Proclaiming himself "The Greatest" the brash fighter earned the nickname "Louisville Lip."

In 1964, Clay got a shot at the heavyweight title against champion Sonny Liston. Leading up to the contest, Clay said he would "float like a butterfly, sting like a bee." Despite the bravado, odds-makers had Clay as a 7-1 underdog.

On Feb. 25, Clay fought Liston in Miami Beach, Florida. Clay got off to a quick start but at the end of the fourth round complained his eyes were burning and he couldn't see. "I didn't know what the heck was going on," Dundee told NBC Sports years later. "He said, 'Cut the gloves off.'"

Dundee said Liston's corner had used Monsel's Solution (applied to stop bleeding) on the fighter. After Ali's eyes were cleaned, he resumed control of the fight. Liston, who some thought was invincible, couldn't answer the bell for the seventh round. At age 22, Clay was heavyweight champion of the world.

The next day Clay, accompanied by Nation of Islam member Malcolm X, announced at a news conference that he was converting to Islam and changing his name to Cassius X. On March 6, Nation of Islam leader Elijah Muhammad bestowed him the name Muhammad Ali. Muhammad meant one worthy of praise, and Ali was the name of a cousin of the prophet Muhammad.

Ali's proclamation was met with hostility from the mainstream media, many of whom refused to acknowledge his new name. The Nation of Islam preached black pride and black nationalism. Unlike the non-violent teachings of civil rights leader Dr. Martin Luther King, Malcolm X justified violence in the act of self-defense.

On May 25, 1965, Ali defended his title in a rematch with Liston in Lewiston, Maine. The fight lasted only one round and ended with what some thought was a "phantom punch." Ali went on to defend his title eight more times.

In 1966, with the United States becoming more involved militarily in Vietnam, Ali said he was a conscientious objector based on his religious beliefs.

"I ain't got no quarrel with them Viet Cong," he said.

"I'd like for them to say: He took a few cups of love. He took one tablespoon of patience. One tablespoon, teaspoon of generosity. One pint of kindness. He took one quart of laughter. One pinch of concern. And then he mixed willingness with happiness. He added lots of faith. And he stirred it up well. Then he spread it over a span of a lifetime. And he served it to each and every deserving person he met."

Muhammad Ali, when asked in 1972 how he'd like to be remembered

In 1967, shortly before he was to appear at a military facility for induction, Ali said, "Why should they ask me to put on a uniform and go 10,000 miles from home and drop bombs and bullets on brown people in Vietnam while so-called Negro people in Louisville are treated like dogs and denied simple human rights?"

On April 28, in Houston, Ali refused to step forward when his name was called for military service. That same day the New York State Athletic Commission suspended his boxing license and stripped him of his title. Other boxing commissions followed suit. Soon after, he was convicted of evading the draft, sentenced to five years in prison and fined $10,000.

Ali stayed out of prison while his lawyers filed a series of appeals that eventually reached the Supreme Court.

By 1970, the mood of the country toward the combat in Vietnam was changing with a strong and growing anti-war movement. More people now saw Ali's refusal to be drafted not as the act of a traitor, but as a legitimate reaction against what they thought was an unjust conflict.

Eight months before the court ruled, Ali was able to land a fight with highly rated heavyweight Jerry Quarry. The fight would be held in Atlanta. The state didn't have an athletic commission and with the approval of the mayor, the fight was green-lighted despite the objections of segregationist governor Lester Maddox.

On Oct. 26, 1970, 43 months after his last fight, Ali made a triumphant return to the ring. Despite showing some rust, Ali bloodied Quarry, winning on a third-round TKO.

While Ali was banished from boxing, Joe Frazier became the heavyweight champion. During Ali's boxing exile, Frazier had supported his attempts to return to the sport. An agreement was reached for the two to fight. In the buildup, Ali called Frazier an "Uncle Tom," something Frazier would never forget or forgive.

On March 8, 1971, they fought at Madison Square Garden in "The Fight of the Century." The bout was between the current undefeated champion and the undefeated former title holder whose fans still considered him the real champ. What followed was a 15-round epic with Frazier knocking Ali down in the 15th round en route to a unanimous decision win.

On June 28, 1971, it was Ali's turn to win a unanimous decision when the Supreme Court overturned his draft evasion conviction.

There was great anticipation for a championship rematch but circumstances changed that in 1973. In January, Frazier lost his title when he was savagely defeated in two rounds by George Foreman in Kingston, Jamaica. Two months later, Ali had his jaw broken in a loss to Ken Norton in San Diego.

Ali avenged his loss to Norton and added a win over Ruddi Lubbers while Frazier won his next fight over Joe Bugner, setting up Ali/Frazier II. On Jan. 28, 1974, the second Ali-Frazier bout was scheduled to take place at Madison Square Garden. Just days before they were to fight, the boxers appeared on ABC's "Wide World of Sports" with Howard Cosell. An argument ensued, with Ali calling Frazier "ignorant." Frazier countered, "I'm not ignorant!"

That led to the two wrestling on the studio floor before they were separated.

The real fight was billed as "Super Fight II" and was for the North American Boxing Federation championship. But the real prize was for the winner to get a shot at champion George Foreman. Ali won the fight with a 12-round unanimous decision.

Ali was 32 on Oct. 30, 1974, when he faced the 25-year- old Foreman for what became known as "The Rumble in the Jungle." The fight was held in Kinshasa, Zaire. To accommodate viewers in the United States, the contest began at 4 a.m. local time. Foreman was 40-0 with 37 knockouts, including a two-round demolition of Ken Norton earlier that year. There was concern by some that Foreman would kill Ali. With the crowd chanting "Ali bomaye!," (Ali, kill him!), Ali unveiled a strategy that would turn the bout.

Starting in the second round he stayed along the ropes, allowing Foreman to throw a series of punches that were mainly blocked by his arms. The "rope-a-dope" tactic sapped Foreman's energy in the tropical heat. But Ali was also absorbing a great deal of punishment. In the eighth round, he came off the ropes and landed a series of punches that sent the exhausted Foreman to the canvas. Ali had regained the heavyweight title in an unlikely victory.

Following the death of Elijah Muhammad, Ali left the Nation of Islam and converted to Sunni Islam.

Ali defended his title three more times before his third and final fight against Joe Frazier. The "Thrilla in Manila" took place Oct. 1, 1975, in Manila, Philippines. It would be the most brutal of the trilogy, a battle that would test the limits of their wills.

As was the case in the previous two encounters, Ali belittled Frazier leading up to the fight. At one news conference he said, "It's gonna be a chilla, and a killa, and a thrilla, when I get the Gorilla in Manila."

The fight began with Ali unleashing a flurry of punches that landed on Frazier. But Frazier wouldn't back down. By the middle rounds Frazier was taking over the fight. Ali survived the onslaught and in the eleventh was able to unleash several combinations that caused severe swelling around the challenger's eyes. Taking advantage of Frazier's condition, Ali continued to connect, and in the 13th round, he knocked out Frazier's mouthpiec. At the end of the 14th round, both men were exhausted, but with Frazier unable to see, his corner stopped the fight. Ali was barely able to get off his stool to acknowledge the victory. Years later, Ali described the fight "as the closest thing to dying."

Ali was 36 when he faced 24 year-old Leon Spinks on Feb. 15, 1978 in Las Vegas. Like Ali, Spinks was an Olympic light heavyweight gold medal-winner. Spinks was a 10-1 underdog as he faced Ali in only his eighth pro fight but won a 15th-round split decision. Some thought it was the end of Ali's career; it wasn't.

Seven months after losing his belt, Ali took it back. On Sept. 15, an estimated 90 million people viewed ABC's telecast of Ali-Spinks II, with another 60,000 watching inside the Louisiana Superdome. Ali took a 15-round unanimous decision and became the first man to win the heavyweight title three times.

In June 1979, Ali retired from boxing. Unfortunately for him and his fans, he decided to unretire.

In early 1980, he agreed to fight new WBA heavyweight champion John Tate. But Tate lost the belt to Mike Weaver in March. In July, following one failed attempt, Ali signed on to fight WBC champion Larry Holmes in Las Vegas.

Due to concerns about his health, the Nevada State Athletic Commission had Ali examined at the Mayo Clinic as a prerequisite to receiving a boxing license. In his book "Muhammad Ali: His Life and Times," Thomas Hauser obtained a copy of the findings that indicated Ali had difficulty controlling facial muscles in speech.

"The remainder of his examination is normal except that he does not quite hop with the agility that one might anticipate, and on finger-to-nose testing there is a slight degree of missing the target. Both of these tests could be significantly influenced by fatigue," the report said. "There is no specific finding that would prohibit him from engaging in further prizefights."

As a result, the 38-year old Ali was granted a boxing license.

The Oct. 2 fight was never in doubt. Holmes was 8 years younger and had a 35-0 record entering the contest. Though Ali wasn't knocked down, Holmes dominated, winning every round on the judges' cards. Ali's corner stopped it after the 10th.

A few days after the fight, Ali was examined at UCLA Medical Center, where doctors said the boxer suffered "residual damage" from the one-sided contest. Ali said at a news conference he checked himself into the facility " to stop rumors about my being hurt — brain damaged or kidney damaged." But he also revealed he was taking Thyrolar for a thyroid condition at double the prescribed amount. Ali claimed that sapped his strength contributing to his defeat. His doctor, Dr. Charles Lee Williams Sr., said he prescribed Thyrolar for a thyroid imbalance, but couldn't say how he came to that conclusion. Some suspected Ali took Thyrolar to lose weight, which can happen with overdosing the medication.

Ali weighed in at 217½ pounds, the lightest he'd been since the Foreman fight. Ali said, " I shall return." That return would be against 28 year-old Trevor Berbick, a Jamaican fighting out of Canada. Berbick had lost a 15-round decision to Holmes in April 1981, for the WBC heavyweight title. But with concerns over Ali's health and diminished boxing skills, state athletic commissions wouldn't issue him a license.

There were claims, including from his former cornerman, Dr. Ferdie Pacheco, that Ali had suffered brain damage from fighting. Ali submitted to a series of tests before the fight at New York University. The tests were supervised by Dr. Harry Demopoulos, who told Sports Illustrated that 30 doctors were involved.

"There's absolutely no evidence that Muhammad has sustained any injury to any vital organ — brain, liver, kidneys, heart, lungs — nervous system, or muscle or bone systems. His blood tests indicate he has the vessels of a young man," Demopoulos said. He also called Ali's slurred speech "psychosocial response."

The Bahamas approved the fight.

On Dec. 11, 1981, Ali lost a 10-round unanimous decision to Berbick in his final fight, a lackluster performance that even Ali realized was a sign of his reduced capabilities.

"My timing and reflexes just wasn't there,' he told reporters after the fight. "There were things that I wanted to do but just couldn't. No, I'm certain this time. At the Holmes fight I had excuses. This time I had no excuses. I know myself better than anybody and I know this is the end."

Ali finished his professional career with a 56-5 record, including 37 knockouts. He was inducted into the International Boxing Hall of Fame in 1990.

"We lost a giant today," Manny Pacquaio said in a statement. "Boxing benefited from Muhammad Ali's talents but not nearly as much as mankind benefited from his humanity. Our hearts and prayers go out to the Ali family. May God bless them."

In 1984, it was revealed that the 42-year-old Ali had Parkinson's syndrome. He had tremors, slurred speech and slow body movements. Doctors said it was the result of injuries to the brain sustained during his boxing career.

In the following years, Ali's condition deteriorated but he remained active as a humanitarian and goodwill ambassador. The man who used to fight in the ring now traveled the world fighting racism, hunger and poverty. Ali supported many charities and causes, including research into Parkinson's disease, supplying medicine to the needy and improving literacy rates.

In 1990, against the wishes of the U.S. government, he traveled to Iraq and won the release of 15 American hostages who were being held by dictator Saddam Hussein.

In 1996, Ali was given the honor of lighting the Olympic cauldron at the Atlanta Games.

Ali served for 10 years as United Nations Messenger of Peace. In 2005, he won the Presidential Medal of Freedom, the nation's highest civilian award.

ESPN had ranked Ali as the third greatest athlete of the 20th century, behind Michael Jordan (No. 1) and Babe Ruth.

"We are sad to hear of the passing of Muhammad Ali. However, we revel in the memory of his athletic excellence in the ring, we recollect with pleasure the charm of the charismatic young man from Louisville who would shock the world and we celebrate the dramatic achievement of a champion of civil rights who changed the world," ESPN President John Skipper said in a statement. "In many ways, he was truly the greatest of all time."

Tennis Hall of Famer and social activist Arthur Ashe summed up Ali's contribution to American race relations in an interview with Thomas Hauser.

"Ali didn't just change the image that African Americans have of themselves," Ashe said. "He opened the eyes of a lot of white people to the potential of African Americans; who we are and what we can be."

In a 1972 interview with David Frost, Ali was asked, "What would you like people to think about you when you're gone?"

Ali answered: "I'd like for them to say: He took a few cups of love. He took one tablespoon of patience. One tablespoon, teaspoon of generosity. One pint of kindness. He took one quart of laughter. One pinch of concern. And then he mixed willingness with happiness. He added lots of faith. And he stirred it up well. Then he spread it over a span of a lifetime. And he served it to each and every deserving person he met."