In the 1950s, economist JK Galbraith cautioned that corporations were becoming too powerful and in the 1960s he warned President John F Kennedy about the dangers of unilateral military action abroad.
Galbraith continually criticised conservative administrations' fiscal policies and tried to bring environmental issues into the limelight.
"He was a half of a century ahead of his time," said his biographer, Richard Parker.
Galbraith, a Harvard economist and behind-the-scenes political adviser to Democratic presidents, died late on Sunday of natural causes, his son said.
His influence remained relevant long after his 1958 work The Affluent Society argued that the American economy produced individual wealth but did not adequately address public needs such as schools.
Advised Presidents
British Finance Minister Gordon Brown said Galbraith advised him and others in recent years with insights into the modern age.
"Even in recent years in his 90s he was never slow to give me and others advice and he will be remembered for his erudition, his wit and eloquence and particularly for his economic insights into our age," Mr Brown said.
The Canadian-born economist and unabashed liberal served as adviser to Democratic presidents from Franklin D Roosevelt to Bill Clinton and was John F Kennedy's ambassador to India.
Galbraith, who was outspoken in his support of government intervention in social and economic problems, became a larger figure on the American political scene after World War II.
Senator Edward Kennedy lauded Galbraith's profound commitment to social justice. “I know how much President Kennedy admired his genius, valued his friendship and loved his extraordinary wit, and so did I," the Democrat said.
"Our affluent society is a fairer and more just society today because of Ken, and no one who knew him will ever forget him."
Although an economist, his impact reached far beyond economic circles. He thought across disciplines, Benjamin Freeman, a Harvard economics professor and friend of Galbraith's said, "not just in the field (of economics), but broadening the discourse to encompass the world at large."
It was this integration of different topics that gave Galbraith unique foresight about politics and economics in America, said Professor Parker, who wrote John Kenneth Galbraith: His Life, His Politics, His Economics.
’Moralist and controversialist’
A review of Professor Parker's biography in the March edition of the
Journal of Economic Literature argued that, although Galbraith was the "best known" economist in the 50s and 60s, "he was not then, and will never be, regarded as a great economist by economists, because he produced no theories, which is what great economists are supposed to do," wrote University of Warwick economist Robert
Skidelsky.
He described Galbraith as an "eminent public figure - moralist, controversialist, stylist, wit - who happened to profess economics."
But former Harvard President Derek Bok said Galbraith was distinct from other economists because he wrote for a general audience, something that critics have cited as a weak spot.
"He used his wit ... very tellingly to make points about society," Bok said. "He was not one to express anger. But he was an expert in using his wit to attack (people he disagreed with) by making people laugh."
After graduating from the University of Toronto in 1931, Galbraith moved to the US where he earned his PhD in economics from the University of California.
He taught at Harvard from 1934 to 1939 and at Princeton University from 1939 to 1942, returning to Harvard in 1948, remaining active on the faculty until his retirement in 1975.
Galbraith was married in 1937 to Catherine Atwater. They had three sons, Alan, Peter and James. Services have not yet been scheduled.
"His mind was wonderful, right up until the end," Alan Galbraith said. "He had a wonderful and full life."