LOS ANGELES - An outpouring of grief and homage greeted word that Oscar-winning actor and comedian Robin Williams had apparently taken his own life after a battle with depression.
The 63-year-old known for high-energy, rapid-fire improvisation and clowning was one of the most beloved entertainers of his time. One publication once called him the funniest man alive.
The star of films such as "Good Will Hunting," "Good Morning Vietnam" and "Mrs Doubtfire" was found dead at his home in Tiburon, in California just north of San Francisco, shortly before midday on Monday, police said.
President Barack Obama led tributes to an entertainer he described as "one of a kind", while Hollywood titan Steven Spielberg, a close friend, hailed Williams as a "lightning storm of comic genius."
A statement from Marin County Sheriff's Department said Williams' death appeared to be "suicide due to asphyxia."
An autopsy is scheduled for Tuesday, followed by further toxicology testing, the statement said.
Described in 1997 by showbiz publication Entertainment Weekly as "the funniest man alive", Williams had in fact been suffering from depression prior to his death, his publicist said.
The comedian himself had spoken openly in the past about his battles with alcoholism and drug abuse.
"Robin Williams passed away this morning. He has been battling severe depression of late," Mara Buxbaum said in a statement on Monday.
Wife Susan Schneider urged the father-of-three's millions of fans to remember his talent at making people laugh.
"This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings," said Schneider, who became the actor's third wife when the couple married in 2011.
"I love you. I miss you. I'll try to keep looking up," Williams's daughter Zelda said in a message that appeared alongside a quote from French writer and aviator Antoine de Saint-Exupery.
A file picture taken on January 22, 1994 in Beverly Hills, shows US actor Robin Williams posing with his best actor in a musical or comedy award during the Golden Globe ceremony. AFP PHOTO / DAVID CRANE
Apparently alluding to his own troubles with drugs, Williams once said, "cocaine is God's way of telling you you are making too much money."
After beginning his career as a stand-up comic, Williams rose to fame in the iconic US television sitcom "Mork & Mindy", channelling his anarchic, high-energy style to his role as an extra-terrestrial struggling to fit in on Earth.
He later reeled off a string of big-screen hits throughout the 1980s and 1990s in roles which often showcased his phenomenal fast-talking, improvisational skills.
Those abilities were showcased in 1987's "Good Morning, Vietnam", where his performance as motormouth military disc jockey Adrian Cronauer earned him the first of four career Oscar nominations.
But while that role could have been tailored for Williams' comic skills, he also earned critical plaudits in weightier dramas.
He added more Oscar nominations for his performance as the inspirational English literature teacher John Keating in 1989's "Dead Poets Society" and for playing a mentally ill homeless man mourning the loss of his wife in 1991's "The Fisher King."
He finally landed a coveted Oscar for 1997's "Good Will Hunting," which earned him a best supporting actor statuette, and helped launch the Hollywood careers of co-stars Matt Damon and Ben Affleck.
News of Williams' death quickly supplanted the conflict in Iraq as the top item on evening news bulletins as Americans reacted with shock.
A fan holds a photo of himself with the actor at Robin Williams' star on the Hollywood Walk of Fame, August 11, 2014, in Hollywood, California. AFP PHOTO/Mark RALSTON
One of a kind': Obama
Obama, on holiday in Martha's Vineyard, spoke of Williams' array of beloved performances as he led the tributes to the entertainer.
"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, " Obama said in a statement.
"He arrived in our lives as an alien -- but he ended up touching every element of the human spirit," he added, referring to Williams' breakthrough television role as the extraterrestrial visitor Mork.
"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 marginalized on our own streets."
Spielberg paid tribute to "a comic genius."
"Robin was a lightning storm of comic genius and our laughter was the thunder that sustained him," said the director.
"He was a pal and I can't believe he's gone," added Spielberg, who famously regularly phoned Williams to cheer himself up during filming of his harrowing 1994 Holocaust drama "Schindler's List."
Spielberg's tribute was echoed throughout an entertainment industry left reeling by news of the comedian's death.
"I can't believe the news about Robin Williams. He gave so much to so many people. I'm heartbroken," comic and talkshow host Ellen DeGeneres said on Twitter.
Fellow comedian Steve Martin added: "I could not be more stunned by the loss of Robin Williams, mensch, great talent, acting partner, genuine soul."
'Harry Potter' actor found dead in Death Valley
Suit filed in death of 'Fast and Furious' actor Paul Walker