Although famous for his hyperactive comedy brain, Williams spent much of his life battling alcoholism, drug abuse and depression. His final bout of depression, which several weeks in a rehabilitation clinic had failed to lift, may have been triggered in part by the cancellation of his latest television show, The Crazy Ones, in May, after just one series.
According to a family friend quoted by the US website Radar Online: "All he could talk about were serious money troubles ... Robin was known for being so generous to his friends and family during the height of his success, and would help anyone out that needed it.
"There was also frustration that Robin expressed at having to take television and movie roles he didn't want to take, but had to for the pay cheque."
For two years he had been trying to sell his ranch in the Napa Valley near San Francisco, saying: "I just can't afford it any more."
Despite dropping the asking price from $42 million to $35.6 million, there had been no takers.
He had even resorted to selling some of his collection of 50 bicycles to raise cash.
One neighbour who saw him in the days before his death said he had become "a shell of himself" and looked "drawn and thin".
Last September Williams, who had moved into a relatively modest bungalow in Tiburon, near San Francisco, which he inherited from his mother in 2001, told about having to "downsize" his life and said he faced the choice of a stand-up comedy tour, returning to television after 31 years, or taking roles in low-budget films for very low pay.
He went on: "Divorce is expensive. I used to joke they were going to call it 'all the money' but they changed it to 'alimony'. It's ripping your heart out through your wallet."
Williams' two divorces are reported to have cost him $40 million, and he had put a substantial sum into trust funds for his three children, Zachary, 31, Zelda, 25, and Cody, 22.
Stellan Skarsgard, who appeared with him in the Oscar-winning Good Will Hunting in 1997, said: "People take their own lives for many different reasons, and it's not unusual among comedians that the comedy is a way of keeping the darkness at bay."
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Williams' close friend and fellow comic actor Chevy Chase said: "Robin and I were great friends, suffering from the same little-known disease: depression. I never could have expected this ending to his life ... I cannot believe this. I am overwhelmed with grief."
Lieutenant Keith Boyd, assistant deputy chief coroner of Marin County, said Williams was last seen alive at 10.30pm local time on Sunday when his wife, Susan Schneider, went to bed. She left at 10.30am assuming Williams was still asleep in another bedroom.
He was found dead by his personal assistant at 11.55am when there was no response to knocks on his bedroom door.
Mr Boyd said the actor was "clothed" and looked to have been dead for some time.
He added that toxicology reports, which will show whether Williams had drugs or alcohol in his body, would take at least two weeks to prepare.
Williams overcame alcohol and drug addiction in the 80s, and had remained sober apart from a spell when he began drinking again and went to rehab in 2006.
In an interview in 2010 Williams said he had thought seriously about suicide only once, but told himself: "Have you noticed that things are pretty good even though you're not working right now?"
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (4pm to 6pm weekdays)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.
