Kenneth Lay, the former Enron chief executive and chairman convicted on fraud and conspiracy charges, has died.
Mr Lay was awaiting sentencing after being convicted of fraud
Mr Lay suffered a heart attack at his holiday home near Aspen, Colorado. He was pronounced dead in hospital shortly after 0300 local time on Wednesday.
He and former chief executive Jeffrey Skilling were found guilty in May in connection with Enron's collapse.
The US energy giant went bankrupt in 2001 with debts of $31.8bn (£18bn), leaving 4,000 people out of work.
After America's most high-profile corporate fraud trial, Mr Lay was found guilty on 25 May on all six fraud and conspiracy charges that he faced.
THE ENRON SAGA IN FIGURES
$101bn: Enron's claimed revenues in 2000
$31.8bn: The size of Enron's debts when it went bankrupt in 2001
$252m: The amount, including stock options, that Kenneth Lay earned in his best year at Enron
$100m: Mr Lay's peak personal debt. "It was difficult to turn off that lifestyle like a spigot," he once said
$75m: The sum Mr Lay spent on shares illegally bought using bank loans - he said he did not remember having been told that it was against the law
$40m: Mr Lay's overdraft facility
$23.8m: The fine paid by Andrew Fastow, the former Enron chief financial officer who pleaded guilty to fraud in 2004 and is serving a 10-year jail sentence
$200,000: the cost of hiring a yacht for Mr Lay's wife Linda's birthday party
He had posted a $5m bond to avoid custody until October when he would have been sentenced - to up to 45 years behind bars.
Mr Lay had always proclaimed his innocence, saying the company was brought down by a lack of investor confidence triggered by revelations that Enron's chief financial officer Andrew Fastow had stolen millions from the company.
He described Enron's collapse as "the most devastating and heartbreaking tragedy of my life".
The 64-year-old had led Enron for 15 years from its birth in 1986 after the merger of two Houston-based gas pipeline firms.
From this small beginning, Enron went on to become America's seventh biggest company and the world's largest energy trading firm.
Mr Lay handed the chief executive's role over to Jeffrey Skilling in 2001.
Mr Skilling was convicted on 19 counts of fraud and conspiracy and is expected to face a lengthy prison term.
As well as bringing down Enron and its former bosses, the scandal had a far-reaching effect on corporate America, prompting a re-evaluation of company values and governance.
The Enron scandal, along with the collapse of phone firm Worldcom, was the driving force behind new legislation that holds executives responsible for what happens at the companies they work for.
Today it is no longer enough for chief executives to say they did not know what was happening at their firms.
According to reports, Mr Lay was taken by ambulance from his holiday home in Old Snowmass, Colorado, on Wednesday morning and driven to Aspen Valley Hospital.
He was pronounced dead shortly after 0300 local time (0900 GMT).
"A coroner's autopsy is pending," a county official said. "There will be no further information or press release from this office until autopsy results are available later this week."
Mr Lay is survived by his wife, Linda and five children and step-children.