According to a family friend, pastor Steve Wende, Lay had suffered a massive coronary, but state authorities at the exclusive ski resort of Aspen said the reason for his collapse would be determined by an autopsy.

Lay passed away just six weeks after his criminal conviction on six counts of conspiracy, wire and securities fraud over the collapse of the energy trading multinational, Enron. A jury at a Houston, Texas court found him instrumental in billions of dollars worth of accounting irregularities which prompted the collapse of Enron, once America's seventh largest company with more than $100 billion in annual revenue.

Each of Lay's convictions carried terms of between five and 10 years and he was expected to spend the rest of his life in prison.

Kenneth Lay is survived by wife Linda, five children and 12 grandchildren.

The son of a preacher from a small town in Missouri, Lay was born in Tyrone, Missouri. His parents had little formal education and Lay did what he could to supplement the family income, delivering newspapers and mowing lawns. He followed up an MA in economics from the University of Missouri with a doctorate at the University of Houston in 1970.

Starting his career with Exxon in 1965 as an economist, he also served with the US navy.

He had a brief spell with the US government, serving as under-secretary for energy (1972-74). For the next eight years, he held various executive positions in the oil industry, including, Houston Natural Gas. In 1985, the company merged with a rival, InterNorth, and was renamed Enron. Lay became its chief executive.

Lay transformed the merged entity from a natural gas pipeline company into the biggest name in energy trading. Briefly, Enron even became the seventh largest company in America. Kenneth Lay became a lionised, and much feted man, making it to magazine covers and was the toast of American society. He was nicknamed "Kenny boy" by President Bush and lived a lavish lifestyle with a personal wealth of more than $400 million.

Lay continued as Enron chief executive until February 2001, when he became chairman, making way for his protege, Jeffrey Skilling. Things began to unravel soon thereafter when Skilling, an ex-McKinsey consultant, resigned six months into the job, and Lay stepped back into the chief executive role.

In October 2001, the company rattled Wall Street by reporting losses of $1 billion. By December, the company had filed, for what was then, corporate America's biggest ever bankruptcy. 21,000 people lost their jobs and life savings. Lay and Enron, the toast of corporate America, had became synonymous with corporate fraud.

Lay maintained that the company collapsed due to a sudden loss of confidence among customers and investors, prompted in main by opportunistic short-sellers on the stock market. For prosecutors, however, the company was a financial house of cards with largely illusory profits. The facade of profitability was maintained through increasingly complex accounting tricks dreamed up by Lay, Skilling and their management team.

Lay refused to accept responsibility till the end. Even when he was convicted, he declared, "I firmly believe that I am innocent of the charges against me, as I have said from day one. I still firmly believe that to this day."

His apparent lack of remorse enraged many of those who lost their livelihoods, lifetime savings and investments with Enron. There was, and still remains, much anger in Houston - best exemplified by the roaring trade conducted by an ex-employee in t-shirts with slogans such as "I got Lay'd by Enron."

For some, that might remain Kenneth Lay's enduring legacy.