Actor Robin Williams was found hanged in his bedroom at his California home, an official has said .
The Mrs Doubtfire star was discovered by his personal assistant yesterday morning after he failed to answer his door.
Williams, 63, was last seen alive by his wife Susan Schneider at around 10.30pm on Sunday before she went to bed, Lieutenant Keith Boyd, Marin County's assistant chief deputy coroner, revealed.
She left their home in the town of Tiburon at 10.30am yesterday believing he was still in bed.
But his assistant found the father of three clothed, unconscious and not breathing in his room at about 11.45am, and after the "distraught" woman called emergency services, firefighters pronounced him dead at 12.02pm.
Lt Boyd told reporters in California: "Our indication at this time is that it is a suicide due to asphyxia due to hanging."
The actor had recently grappled with severe depression, and yesterday Williams' family were joined by giants from the world of Hollywood and politics as they mourned his death.
Ms Schneider said she was "utterly heartbroken" and that she had "lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings".
His daughter Zelda Williams, 25, posted an excerpt from French poet and aviator Antoine de Saint-Exupery's The Little Prince on Twitter, which read: "You - you alone will have the stars as no one-else has them... In one of the stars I shall be living. In one of them I shall be laughing. And so it will be as if all the stars were laughing, when you look at the sky at night ... You - only you - will have stars that can laugh."
She added: "I love you. I miss you. I'll try to keep looking up."
Lt Boyd confirmed that Williams had been suffering from depression and the coroner's office had been investigating his medical history.
He said it was not known what time the actor had gone to bed on Sunday, and revealed a forensic examination found he had not suffered any injuries to suggest he had been "in a struggle or altercation".
He also said he would not be discussing "the note" or "a note" as the investigation is on-going.
Lt Boyd said: "The preliminary results of the forensic examination revealed supporting physical signs that Mr Williams' life ended from asphyxia due to hanging.
"Toxicology testing will be conducted to determine if Mr Williams had any chemical substances in his system at his time of death. Toxicology results will not be available for approximately two to six weeks while the testing is being performed.
"Please note this is an active investigation into the cause, manner, and circumstances of Mr Williams' death. The final cause and manner of death will not be certified until the conclusion of the investigation which is several weeks away."
Williams had battled addiction for decades and checked himself back into rehab last month.
But his representative said at the time that he had not fallen off the wagon and was ensuring that he focused on his commitment to stay sober.
Williams shot to fame in the late 1970s as an alien in the US TV comedy series Mork & Mindy.
But it was his role as an irreverent DJ with the US Armed Services Radio station in Good Morning, Vietnam in 1987 which won him huge acclaim.
His roles ranged from serious and dramatic in films such as Dead Poets Society and Good Will Hunting, to comedy in Mrs Doubtfire and Mork & Mindy.
He was Oscar nominated three times before winning an Academy Award for his performance as a psychologist in Good Will Hunting in 1997.
US president Barack Obama led tributes to the star, saying: "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.
"The Obama family offers our condolences to Robin's family, his friends, and everyone who found their voice and their verse thanks to Robin Williams."
The Prince of Wales, who met Williams several times, also paid tribute, saying: "He was a remarkable man, whose wonderful frenetic humour brought a special kind of laughter into people's lives.
"I greatly enjoyed meeting him on several occasions and his irreplaceable contribution to life will be greatly missed by countless people, including myself."
Steven Spielberg, who directed Williams in the 1991 film Hook, called the actor "a lightning storm of comic genius" saying "our laughter was the thunder that sustained him".
"He was a pal and I can't believe he's gone," he added.