Mr. Jackson died at UCLA Medical Center after being stricken at his rented home in Holmby Hills. Paramedics tried to resuscitate him at his home for nearly three-quarters of an hour, then rushed him to the hospital, where doctors continued to work on him.
"It is believed he suffered cardiac arrest in his home. However, the cause of his death is unknown until results of the autopsy are known," his brother Jermaine said. Police said they were investigating, standard procedure in high-profile cases.
Mr. Jackson's death brought a tragic end to a long, bizarre, sometimes farcical decline from his peak in the 1980s, when he was popular music's premier all-around performer, a uniter of black and white music who shattered the race barrier on MTV, dominated the charts and dazzled even more on stage.
His 1982 album Thriller -- which included the blockbuster hits Beat It, Billie Jean and Thriller -- is the best-selling album of all time, with an estimated 50 million copies sold worldwide.
At the time of his death, Mr. Jackson was rehearsing hard for what was to be his greatest comeback: He was scheduled for an unprecedented 50 shows at a London arena, with the first set for July 13.
As word of his death spread, MTV switched its programming to play videos from Mr. Jackson's heyday. Radio stations began playing marathons of his hits. Hundreds of people gathered outside the hospital. In New York's Times Square, a low groan went up in the crowd when a screen flashed that Mr. Jackson had died, and people began relaying the news to friends by cell phone.
"It's like when Kennedy was assassinated," said Michael Harris, 36, of New York City. "I will always remember being in Times Square when Michael Jackson died."
The public first knew him as a boy in the late 1960s, when he was the precocious, spinning lead singer of the Jackson 5, the singing group he formed with his four older brothers out of Gary, Ind. Among their No. 1 hits were I Want You Back, ABC and I'll Be There .
He was perhaps the most exciting performer of his generation, known for his backward-gliding moonwalk, his feverish, crotch-grabbing dance moves and his high-pitched singing, punctuated with squeals and titters. His single sequined glove, tight, military-style jacket and aviator sunglasses were trademarks, as was his ever-changing, surgically altered appearance.
"He was the consummate entertainer and his contributions and legacy will be felt upon the world forever," said Quincy Jones, who produced Thriller . "I've lost my little brother today, and part of my soul has gone with him."
Mr. Jackson ranked alongside Elvis Presley and the Beatles as the biggest pop sensations of all time. He united two of music's biggest names when he was briefly married to Elvis' daughter, Lisa Marie, and Mr. Jackson's death immediately evoked comparisons to Elvis, who died at age 42 in 1977.
As years went by, Mr. Jackson became an increasingly freakish figure -- a middle-age man-child weirdly out of touch with grown-up life. His skin became lighter, his nose narrower, and he spoke in a breathy, girlish voice. He often wore a germ mask while traveling, kept a pet chimpanzee named Bubbles as one of his closest companions, and surrounded himself with children at his Neverland ranch, a storybook playland filled with toys, rides and animals. The tabloids dubbed him "Wacko Jacko."
"It seemed to me that his internal essence was at war with the norms of the world. It's as if he was trying to defy gravity," said Michael Levine, a Hollywood publicist who represented Mr. Jackson in the early 1990s. He called Mr. Jackson a "disciple of P.T. Barnum" and said the star appeared fragile at the time but was "much more cunning and shrewd about the industry than anyone knew."
Mr. Jackson caused a furor in 2002 when he dangled his infant son, Prince Michael II, over a hotel balcony in Berlin while a throng of fans watched from below.
In 2005, he was cleared of charges he molested a 13-year-old cancer survivor at Neverland in 2003. He had been accused of plying the boy with alcohol and groping him, and of engaging in strange and inappropriate behavior with other children.
The case followed years of rumors about Mr. Jackson and young boys. In a TV documentary, he acknowledged sharing his bed with children, a practice he described as sweet and not at all sexual.
Despite the acquittal, the lurid allegations that came out in court took a fearsome toll on his career and image, and he fell into serious financial trouble.
Mr. Jackson was 4 years old when he began singing with his brothers -- Marlon, Jermaine, Jackie and Tito -- in the Jackson 5. After his early success with bubblegum soul, he struck out on his own, generating innovative, explosive, unstoppable music.
The peak might have come in 1983, when Motown celebrated its 25th anniversary with an all-star televised concert and Mr. Jackson moonwalked off with the show, joining his brothers for a medley of old hits and then leaving them behind with a pointing, crouching, high-kicking, splay-footed, crotch-grabbing run through Billie Jean .
The audience stood and roared. Mr. Jackson raised his fist.
By then he had cemented his place in pop culture. He got the plum Scarecrow role in the 1978 movie musical The Wiz , a pop-R&B version of The Wizard of Oz , that starred Diana Ross as Dorothy.
During production of a 1984 Pepsi commercial, Mr. Jackson's scalp suffered burns when an explosion sets his hair on fire.
He had strong follow-up albums with 1987's Bad and 1991's Dangerous , but his career began to collapse in 1993 after he was accused of molesting a boy who often stayed at his home. The singer denied any wrongdoing, reached a settlement with the boy's family, reported to be $20 million, and criminal charges were never filed.
"I am so very sad and confused with every emotion possible. I am heartbroken for his children who I know were everything to him and for his family. This is such a massive loss on so many levels, words fail me." -- Lisa Marie Presley , former wife of Michael Jackson and daughter of Elvis Presley
"I must confess I am not surprised by today's tragic news. Michael has been on an impossibly difficult and often self-destructive journey for years. His talent was unquestionable but so too was his discomfort with the norms of the world. A human simply cannot withstand this level of prolonged stress." -- Michael Leaven , a publicist who represented Mr. Jackson when the singer was accused of molesting a child in 1993
"I knew Michael as a child and watched him grow over the years. Of all the thousands of entertainers I have worked with, Michael was THE most outstanding. Many have tried and will try to copy him, but his talent will never be matched." -- Dick Clark , host of American Bandstand
"Michael Jackson was my generation's most iconic cultural hero. Courageous, unique and incredibly talented. He'll be missed greatly." -- Russell Simmons , hip-hop entrepreneur and founder of Def-Jam Records
"We have lost an icon in our industry and my heartfelt condolences go out to his family and children in this hour of sorrow that they are now going through. He will live on in my memory and most definitely through the music he shared with so many." -- Dionne Warwick , singer and Mr. Jackson's friend
"Michael Jackson was my musical God. He made me believe that all things are possible, and through real and positive music. He can live forever! I love Michael Jackson. God bless him." -- Wyclef Jean , rapper