By ROBERT LIPSYTE | The New York Times

Muhammad Ali, the three-time world heavyweight boxing champion who helped define his turbulent times as the most charismatic and controversial sports figure of the 20th century, died on Friday in a Phoenix-area hospital. He was 74.

His death was confirmed by Bob Gunnell, a family spokesman. The cause was septic shock, a family spokeswoman said.

Ali, who lived near Phoenix, had had Parkinson’s disease for more than 30 years. He was admitted to the hospital on Friday with what Mr. Gunnell said was a respiratory problem.

Ali was the most thrilling if not the best heavyweight ever, carrying into the ring a physically lyrical, unorthodox boxing style that fused speed, agility and power more seamlessly than that of any fighter before him.

But he was more than the sum of his athletic gifts. An agile mind, a buoyant personality, a brash self-confidence and an evolving set of personal convictions fostered a magnetism that the ring alone could not contain. He entertained as much with his mouth as with his fists, narrating his life with a patter of inventive doggerel. (“Me! Wheeeeee!”)

Ali was as polarizing a superstar as the sports world has ever produced — both admired and vilified in the 1960s and ’70s for his religious, political and social stances. His refusal to be drafted during the Vietnam War, his rejection of racial integration at the height of the civil rights movement, his conversion from Christianity to Islam and the changing of his “slave” name, Cassius Clay, to one bestowed by the separatist black sect he joined, the Lost-Found Nation of Islam, were perceived as serious threats by the conservative establishment and noble acts of defiance by the liberal opposition.

Loved or hated, he remained for 50 years one of the most recognizable people on the planet.

In later life Ali became something of a secular saint, a legend in soft focus. He was respected for having sacrificed more than three years of his boxing prime and untold millions of dollars for his antiwar principles after being banished from the ring; he was extolled for his un-self-conscious gallantry in the face of incurable illness, and he was beloved for his accommodating sweetness in public.

In 1996, he was trembling and nearly mute as he lit the Olympic caldron in Atlanta.

That passive image was far removed from the exuberant, talkative, vainglorious 22-year-old who bounded out of Louisville, Ky., and onto the world stage in 1964 with an upset victory over Sonny Liston to become the world champion. The press called him the Louisville Lip. He called himself the Greatest.

Ali also proved to be a shape-shifter — a public figure who kept reinventing his persona.

As a bubbly teenage gold medalist at the 1960 Olympics in Rome, he parroted America’s Cold War line, lecturing a Soviet reporter about the superiority of the United States. But he became a critic of his country and a government target in 1966 with his declaration “I ain’t got nothing against them Vietcong.”

“He lived a lot of lives for a lot of people,” said the comedian and civil rights activist Dick Gregory. “He was able to tell white folks for us to go to hell.”

But Ali had his hypocrisies, or at least inconsistencies. How could he consider himself a “race man” yet mock the skin color, hair and features of other African-Americans, most notably Joe Frazier, his rival and opponent in three classic matches? Ali called him “the gorilla,” and long afterward Frazier continued to express hurt and bitterness.

If there was a supertitle to Ali’s operatic life, it was this: “I don’t have to be who you want me to be; I’m free to be who I want.” He made that statement the morning after he won his first heavyweight title. It informed every aspect of his life, including the way he boxed.

The traditionalist fight crowd was appalled by his style; he kept his hands too low, the critics said, and instead of allowing punches to “slip” past his head by bobbing and weaving, he leaned back from them.

Eventually his approach prevailed. Over 21 years, he won 56 fights and lost five. His Ali Shuffle may have been pure showboating, but the “rope-a-dope” — in which he rested on the ring’s ropes and let an opponent punch himself out — was the stratagem that won the Rumble in the Jungle against George Foreman in 1974, the fight in Zaire (now the Democratic Republic of Congo) in which he regained his title.

His personal life was paradoxical. Ali belonged to a sect that emphasized strong families, a subject on which he lectured, yet he had dalliances as casual as autograph sessions. A brief first marriage to Sonji Roi ended in divorce after she refused to dress and behave as a proper Nation wife. (She died in 2005.) While married to Belinda Boyd, his second wife, Ali traveled openly with Veronica Porche, whom he later married. That marriage, too, ended in divorce.

Ali was politically and socially idiosyncratic as well. After the attacks of Sept. 11, 2001, the television interviewer David Frost asked him if he considered Al Qaeda and the Taliban evil. He replied that terrorism was wrong but that he had to “dodge questions like that” because “I have people who love me.” He said he had “businesses around the country” and an image to consider.

As a spokesman for the Muhammad Ali Center, a museum dedicated to “respect, hope and understanding,” which opened in his hometown, Louisville, in 2005, he was known to interrupt a fund-raising meeting with an ethnic joke. In one he said: “If a black man, a Mexican and a Puerto Rican are sitting in the back of a car, who’s driving? Give up? The po-lice.”

But Ali had generated so much good will by then that there was little he could say or do that would change the public’s perception of him.

“We forgive Muhammad Ali his excesses,” an Ali biographer, Dave Kindred, wrote, “because we see in him the child in us, and if he is foolish or cruel, if he is arrogant, if he is outrageously in love with his reflection, we forgive him because we no more can condemn him than condemn a rainbow for dissolving into the dark. Rainbows are born of thunderstorms, and Muhammad Ali is both.”

Ambition at an Early Age

Cassius Marcellus Clay Jr. was born in Louisville on Jan. 17, 1942, into a family of strivers that included teachers, musicians and craftsmen. Some of them traced their ancestry to Henry Clay, the 19th-century representative, senator and secretary of state, and his cousin Cassius Marcellus Clay, a noted abolitionist.

Ali’s mother, Odessa, was a cook and a house cleaner, his father a sign painter and a church muralist who blamed discrimination for his failure to become a recognized artist. Violent and often drunk, Clay Sr. filled the heads of Cassius and his younger brother, Rudolph (later Rahman Ali), with the teachings of the 20th-century black separatist Marcus Garvey and a refrain that would become Ali’s — “I am the greatest.”

Beyond his father’s teachings, Ali traced his racial and political identity to the 1955 murder of Emmett Till, a black 14-year-old from Chicago who was believed to have flirted with a white woman on a visit to Mississippi. Clay was about the same age as Till, and the photographs of the brutalized dead youth haunted him, he said.

Cassius started to box at 12, after his new $60 red Schwinn bicycle was stolen off a downtown street. He reported the theft to Joe Martin, a police officer who ran a boxing gym. When Cassius boasted what he would do to the thief when he caught him, Martin suggested that he first learn how to punch properly.

Cassius was quick, dedicated and gifted at publicizing a youth boxing show, “Tomorrow’s Champions,” on local television. He was soon its star.

For all his ambition and willingness to work hard, education — public and segregated — eluded him. The only subjects in which he received satisfactory grades were art and gym, his high school reported years later. Already an amateur boxing champion, he graduated 376th in a class of 391. He was never taught to read properly; years later he confided that he had never read a book, neither the ones on which he collaborated nor even the Quran, although he said he had reread certain passages dozens of times. He memorized his poems and speeches, laboriously printing them out over and over.

In boxing he found boundaries, discipline and stable guidance. Martin, who was white, trained him for six years, although historical revisionism later gave more credit to Fred Stoner, a black trainer in the Smoketown neighborhood. It was Martin who persuaded Clay to “gamble your life” and go to Rome with the 1960 Olympic team despite his almost pathological fear of flying.

Clay won the Olympic light-heavyweight title and came home a professional contender. In Rome, Clay was everything the sports diplomats could have hoped for — a handsome, charismatic and black glad-hander. When a Russian reporter asked him about racial prejudice, Clay ordered him to “tell your readers we got qualified people working on that, and I’m not worried about the outcome.”

“To me, the U.S.A. is still the best country in the world, counting yours,” he added. “It may be hard to get something to eat sometimes, but anyhow I ain’t fighting alligators and living in a mud hut.”

Ali would later cringe at that quotation, especially when journalists harked back to it as proof that a merry man-child had been misguided into becoming a hateful militant.

Of course, after the Rome Games, few journalists followed Clay home to Louisville, where he was publicly referred to as “the Olympic nigger” and denied service at many downtown restaurants. After one such rejection, the story goes, he hurled his gold medal into the Ohio River. But Clay, and later Ali, gave different accounts of that act, and according to Thomas Hauser, author of the oral history “Muhammad Ali: His Life and Times,” Clay had simply lost the medal.

Clay turned professional by signing a six-year contract with 11 local white millionaires. (“They got the complexions and connections to give me good directions,” he said.) The so-called Louisville Sponsoring Group supported him while he was groomed by Angelo Dundee, a top trainer, in Miami.

At a mosque there, Clay was introduced to the Nation of Islam, known to the news media as “Black Muslims.” Elijah Muhammad, the group’s leader, taught that white people were devils genetically created by an evil scientist. On Allah’s chosen day of retribution, the Mother of Planes would bomb all but the righteous, and the righteous would be spirited away.

Years later, after leaving the group and converting to orthodox Islam, Ali gave the Nation of Islam credit for offering African-Americans a black-is-beautiful message at a time of low self-esteem and persecution. “Color doesn’t make a man a devil,” he said. “It’s the heart and soul and mind that count. What’s on the outside is only decoration.”

Title and Transformation

Clay enjoyed early success against prudently chosen opponents. His outrageous predictions, usually in rhyme — “This is no jive, Cooper will go in five” — put off many older sportswriters, especially since most of the predictions came true. (The Englishman Henry Cooper did go down in the fifth round at Wembley Stadium in 1963, after he had staggered Clay in the fourth.) The reporters’ beau ideal of a boxer was the laconic Joe Louis. But they still wrote about Clay. Younger sportswriters, raised in an age of Andy Warhol, happenings and the “put on,” were delighted by the hype and by Clay’s friendly accessibility.

In 1963, at 21, after only 15 professional fights, he was on the cover of Time magazine. The winking quality of the prose — “Cassius Clay is Hercules, struggling through the twelve labors. He is Jason, chasing the Golden Fleece” — reinforced the assumption that he was just another boxer being sacrificed to the box office’s lust for fresh meat. It was feared he would be seriously injured by the baleful slugger Liston, a 7-to-1 betting favorite to retain his title in Miami Beach, Fla., on Feb. 25, 1964.

But Clay was joyously comic. Encouraged by his assistant trainer and “spiritual adviser,” Drew Brown, known as Bundini, Clay mocked Liston as the “big ugly bear” and chanted a battle cry: “Float like a butterfly, sting like a bee, rumble, young man, rumble.”

The Beatles, on their first American tour, were in town and showed up for a photo op at Clay’s training gym. Malcolm X, a leading minister for the Nation of Islam and a worrisome presence to many white Americans, was there, too, with his family members as guests of Clay, whom they saw as a big brother.

To the shock of the crowd, Clay, taller and broader than Liston at 6 feet 3 inches and 210 pounds and much faster, took immediate control of the fight. He danced away from Liston’s vaunted left hook and peppered his face with jabs, opening a cut over his left eye. Clay was in trouble only once. Just before the start of the fifth round, his eyes began to sting. It was liniment, but he suspected poison. Dundee had to push him into the ring. Two rounds later, Liston, slumped on his stool, his left arm hanging uselessly, gave up. He had torn muscles swinging at Clay in vain.

Clay, the new champion, capered along the ring apron, shouting at the press: “Eat your words! I shook up the world! I’m king of the world!”

(More than a year later, in May 1965, he would retain his crown in lightning-quick fashion in a rematch with Liston in Lewiston, Me. Within two minutes of the first round, Ali threw what became known as the phantom punch, sending Liston sprawling and resulting in a disputed decision to end the fight.)

The morning after the Miami Beach fight, a calm Clay affirmed his rumored membership in the Nation of Islam. He would be Cassius X. (A few weeks later he became Muhammad Ali, which he said meant “Worthy of all praise most high.”) That day he harangued his audience with a preview of what would, over the next few years, become a series of longer and more detailed lectures about religion and race. This one was about, as he put it, “staying with your own kind.”

“In the jungle, lions are with lions and tigers with tigers,” he said. “I don’t want to go where I’m not wanted.”

The only prominent leader to send Ali a telegram of congratulations was the Rev. Dr. Martin Luther King Jr.

“I remember when Ali joined the Nation of Islam,” Julian Bond, the civil rights activist and politician, once said. “The act of joining was not something many of us particularly liked. But the notion he’d do it — that he’d jump out there, join this group that was so despised by mainstream America, and be proud of it — sent a little thrill through you.”

The thrills gave way to darker thoughts. After Malcolm X left the Nation and was assassinated on Feb. 21, 1965, by members of the group, there was talk that Ali had been tacitly complicit. Jack Newfield, a political journalist with an interest in boxing, wrote, “If Ali, as the new heavyweight champion, had remained loyal to his mentor, and continued to lend his public support to Malcolm, history might have gone in a different direction.”

Refusing to Be Drafted

On Feb. 17, 1966, a day already roiled by the Senate’s televised hearings on the war in Vietnam, Ali learned that he had been reclassified 1A by his Louisville selective service board. He had originally been disqualified by a substandard score on a mental aptitude test. But a subsequent lowering of criteria made him eligible to go to war. The timing, however, was suspicious to some; the contract with the Louisville millionaires had run out, and Nation members were taking over as Ali’s managers and promoters.

“Why me?” Ali said when reporters swarmed around his rented Miami cottage to ask about his new draft status. “I buy a lot of bullets, at least three jet bombers a year, and pay the salary of 50,000 fighting men with the money they take from me after my fights.”

But as the reporters continued to press him with questions about the war, the geography of Asia and his thoughts about killing Vietcong, he snapped, “I ain’t got nothing against them Vietcong.”

The remark was front-page news around the world. In America, the news media’s response was mostly unfavorable, if not hostile. The sports columnist Red Smith of The New York Herald Tribune wrote, “Squealing over the possibility that the military may call him up, Cassius makes himself as sorry a spectacle as those unwashed punks who picket and demonstrate against the war.”

Most of the press refused to refer to Ali by his new name. When two black contenders, Floyd Patterson and Ernie Terrell, insisted on calling him Cassius Clay, Ali taunted them in the ring as he delivered savage beatings.

On April 28, 1967, Ali refused to be drafted and requested conscientious-objector status. He was immediately stripped of his title by boxing commissions around the country. Several months later he was convicted of draft evasion, a verdict he appealed. He did not fight again until he was almost 29, losing three and a half years of his athletic prime.

They were years of personal and intellectual growth, however, as Ali supported himself on the college lecture circuit, offering medleys of Muslim dogma and boxing verse. In the question-and-answer sessions that followed, Ali was forced to explain his religion, his Vietnam stand and his opposition (unpopular on most campuses) to marijuana and interracial dating. Now the “onliest boxer in history that people asked questions like a senator” developed coherent answers.

During his exile from the ring, Ali starred in a short-lived Broadway musical, “Big Time Buck White,” one of several commercial ventures. There was a fast-food chain called Champburger and a mock movie fight with the popular former champion Rocky Marciano in which Ali outboxed the slugger until being knocked out himself in the final round. The broadcaster Howard Cosell, one of Ali’s most steadfast supporters in the news media, was responsible for keeping him on television, both as an interview subject and as a commentator on boxing matches.

As Ali’s draft-evasion case made its way to the United States Supreme Court, he returned to the ring on Oct. 26, 1970, through the efforts of black politicians in Atlanta. The fight, which ended with a quick knockout of the white contender Jerry Quarry, was only a tuneup for Ali’s anticipated showdown with Frazier, the new champion. But it was a night of glamour and history as Coretta Scott King, Bill Cosby, Diana Ross, the Rev. Jesse Jackson and Sidney Poitier turned out to honor Ali. The Rev. Ralph Abernathy presented him with the annual Dr. King award, calling him “the March on Washington all in two fists.”

“The Fight,” as the Madison Square Garden bout with Frazier on March 8, 1971, was billed, lived up to expectations as an epic match. With Norman Mailer ringside taking notes for a book and Frank Sinatra shooting pictures for Life magazine, Ali stood toe to toe with Frazier and slugged it out as if determined to prove that he had “heart,” that he could stand up to punishment. Frazier won a 15-round decision. Both men suffered noticeable physical damage.

To Ali’s boosters, the money he had lost standing up for his principles and the beating he had taken from Frazier proved his sincerity. To his critics, the bloody redemption meant he had finally grown up. The Supreme Court also took a positive view. On June 28, 1971, it unanimously reversed a lower court decision and granted Ali his conscientious-objector status.

Resurgence and Decline

It was assumed now that Ali’s time had passed and that he would become a high-grade “opponent,” the fighter to beat for those establishing themselves. But his time had returned. Although he was slower, his artistry was even more refined. “He didn’t have fights,” wrote Jim Murray of The Los Angeles Times, “he gave recitals.”

He won 13 of his next 14 fights, including a rematch with Frazier, who had lost his title to George Foreman, a bigger, more frightening version of Liston.

Ali was the underdog, smaller and seven years older than Foreman, when they met on Oct. 30, 1974, in Zaire, then ruled by Mobutu Sese Seko. Each fighter was guaranteed $5 million, an extraordinary sum at the time. The fight also launched the career of the promoter Don King and was the subject of Leon Gast’s documentary “When We Were Kings,” which was released more than 20 years later. (Ali attended a special screening, along with hip-hop performances, at Radio City Music Hall.) The film won a 1997 Academy Award.

Ali reveled in the African setting, repeating an aphorism he had heard from Brown, his assistant trainer: “The world is a black shirt with a few white buttons.”

As the fight progressed, the crowd chanted, “Ali, bomaye!” (“Ali, kill him!”), first out of concern as Ali leaned against the ropes and absorbed Foreman’s sledgehammer blows on his arms and shoulders, and then in mounting excitement as Foreman wore himself out. In the eighth round, in a blur of punches, Ali knocked out Foreman to regain the title. He leaned down to reporters and said, “What did I tell you?”

On Dec. 10, 1974, Ali was invited to the White House for the first time, by President Gerald R. Ford, an occasion that signified not only a turning point in the country’s embrace of Ali but also a return of the Lip. Ali told the president, “You made a big mistake letting me come because now I’m going after your job.”

Ali successfully defended his title 10 times over the next three years, at increasing physical cost. He knocked out Frazier in their third match, the so-called Thrilla in Manila in 1975, but the punishment of their 14 rounds, Ali said, felt close to dying.

In 1978 he lost and then regained his title in fights with Leon Spinks. Ali’s longtime ring doctor, Ferdie Pacheco, urged him to quit, noting the slowing of his reflexes and the slurring of his speech as symptoms of damage. Ali refused. In 1980, he was battered in a loss to the champion Larry Holmes. A year later, he fought for the last time, losing to the journeyman Trevor Berbick in the Bahamas.

Ali was soon told that he had Parkinson’s syndrome. Several doctors have speculated that it was brought on by too many punches to the head. The diagnosis was later changed to Parkinson’s disease, according to his wife, Lonnie. She said it had been brought on by Ali’s exposure to pesticides and other toxic chemicals at his training camp in Deer Lake, Pa.

A Champion Is Celebrated

After retiring from the ring, Ali made speeches emphasizing spirituality, peace and tolerance, and undertook quasi-diplomatic missions to Africa and Iraq. Even as he lost mobility and speech, he traveled often from his home in Berrien Springs, Mich. Product and corporate endorsements brought him closer to the “show me the money” sensibilities of Michael Jordan and Tiger Woods, the heirs to his global celebrity.

In 1999, Ali became the first boxer on a Wheaties box. On Dec. 31 that year, he rang out the millennium at the New York Stock Exchange. In 2003, a $7,500 art book celebrating his life was published. His life was the subject of a television movie and a feature film directed by Michael Mann, with Will Smith as Ali. (Both productions sanitized his early religious and political viewpoints.) The same licensing firm that owned most of Elvis Presley’s image purchased rights to Ali’s.

Thomas Hauser, his biographer, decried the new “commercialism” surrounding Ali and “the rounding off the rough edges of his journey.” In a book of essays published in 2005, “The Lost Legacy of Muhammad Ali,” Hauser wrote, “We should cherish the memory of Ali as a warrior and as a gleaming symbol of defiance against an unjust social order when he was young.”

In 2005, calling him the greatest boxer of all time, President George W. Bush presented the Medal of Freedom to Ali in a White House ceremony.

In recent years, Parkinson’s disease and spinal stenosis, which required surgery, limited Ali’s mobility and ability to communicate. He spent most of his time at his home in Paradise Valley, Ariz., often watching Western movies and old black-and-white TV shows. He ventured out mostly for physical therapy, movies and concerts. He rarely did TV interviews, his wife said, because he no longer liked the way he looked on camera.

“But he loved the adoration of crowds,” she said. “Even though he became vulnerable in ways he couldn’t control, he never lost his childlike innocence, his sunny, positive nature. Jokes and pranks and magic tricks. He wanted to entertain people, to make them happy.”

Correction: June 4, 2016 An earlier version of a graphic with this article misstated the publication date of when Cassius Clay won an Olympic gold medal. It was Sept. 7 1960, not 1920.