Actor Robin Williams has died in an apparent suicide at the age of 63.
He was a brilliant shapeshifter who could channel his frenetic energy into delightful comic characters like Mrs Doubtfire or harness it into richly nuanced work like his Oscar-winning turn in Good Will Hunting.
He was pronounced dead at his home in the San Francisco Bay area, according to the sheriff's office in Marin County, north of San Francisco.
The sheriff's office said the preliminary investigation showed the cause of death to be a suicide due to asphyxia.
The Marin County coroner's office said Williams was last seen alive at home at about 10pm on Sunday. An emergency call from his house in Tiburon was placed to the Sheriff's Department shortly before noon yesterday.
The actor's wife, Susan Schneider, said: "This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings. I am utterly heartbroken.
"On behalf of Robin's family, we are asking for privacy during our time of profound grief. As he is remembered, it is our hope the focus will not be on Robin's death, but on the countless moments of joy and laughter he gave to millions."
Williams had been battling severe depression recently, said Mara Buxbaum, his press representative.
Just last month, he announced he was returning to a 12-step treatment programme he said he needed after 18 months of non-stop work. He had sought treatment in 2006 after a relapse following 20 years of sobriety.
An Irishman who helped Robin Williams cope with alcoholism believes the actor was tormented with inner conflict.
Anthony Murray, a native of Co Meath, ran the 'Dry Dock' in San Francisco where the actor attended to maintain sobriety.
The Irish sober-living coach has said that despite his shy and quiet nature, Mr Murray said he got the impression he was troubled.
Mr Murray coincidentally met the actor first decades earlier in a bar.
"I met Robin probably in 1982 in the Richmond district of San Francisco, where he was still doing stand-up comedy", he said.
However it was when the star began attending the dry dock in 2005 that he gained his unique insight.
"I think what happened to Robin was that he stopped cold turkey and he did it on his own, I think he was dry for around 20 years.
"He started coming to the meetings around 2005. I think there was a big expose story in the tabloids that he relapsed.
"He would share in the meetings about his difficulties, just like everyone else. The whole strategy is all about anonymity and humility."
From his breakthrough in the late 1970s as the alien in the hit TV comedy Mork & Mindy, through his stand-up comedy act and such films as Good Morning, Vietnam, the short, barrel-chested Williams ranted and shouted as if just sprung from solitary confinement. Loud, fast and manic, he parodied everyone from John Wayne to Keith Richards, impersonating a Russian immigrant as easily as a pack of Nazi attack dogs.
He was a riot in drag in Mrs Doubtfire, or as a cartoon genie in Aladdin. He won his Academy Award in a rare dramatic role, as an empathetic therapist in the 1997 film Good Will Hunting.
He was no less on fire in interviews. During a 1989 chat with the Associated Press, he could barely stay seated in his hotel room, or even mention the film he was supposed to promote, as he free-associated about comedy and the cosmos.
"There's an Ice Age coming," he said. "But the good news is there'll be daiquiris for everyone and the Ice Capades will be everywhere. The lobster will keep for at least 100 years, that's the good news. The Swanson dinners will last a whole millennium. The bad news is the house will basically be in Arkansas."
As word of his death spread, tributes from inside and outside the entertainment industry poured in.
President Barack Obama said in a statement: "Robin Williams was an airman, a doctor, a genie, a nanny, a president, a professor, a bangarang Peter Pan, and everything in between. But he was one of a kind. He arrived in our lives as an alien - but he ended up touching every element of the human spirit. He made us laugh. He made us cry.
"He gave his immeasurable talent freely and generously to those who needed it most - from our troops stationed abroad to the marginalised on our own streets."
Following Williams on stage, Billy Crystal once observed, was like trying to top the Civil War.
Like so many funnymen, Williams had dramatic ambitions. He played for tears in Awakenings, Dead Poets Society and What Dreams May Come, which led New York Times critic Stephen Holden to write that he dreaded seeing the actor's "Humpty Dumpty grin and crinkly moist eyes".
But other critics approved, and Williams won three Golden Globes, for Good Morning, Vietnam, Mrs Doubtfire and The Fisher King.
His other film credits included Robert Altman's Popeye, Paul Mazursky's Moscow On The Hudson, Spielberg's Hook and Woody Allen's Deconstructing Harry.