Irving Kristol's right-wing ideas held sway for two decades
The man known as the "godfather of neoconservatism", Irving Kristol, has died from lung cancer at the age of 89.
Mr Kristol rejected the communist beliefs of his youth to become a leading right-wing thinker and writer.
His ideas had a huge influence on the Bush administration and in 2002 he was awarded the Presidential Medal of Freedom by President George W Bush.
The magazine edited by his son William Kristol, The Weekly Standard, paid tribute to his "wisdom" and "wit".
It added that his "generosity of spirit made him a friend and mentor to several generations of thinkers and public servants".
Irving Kristol was born in the New York borough of Brooklyn, the son of Jewish immigrants from Ukraine.
In the 1930s he was a Trotskyist but he turned his back on his radical left-wing beliefs in favour of liberalism.
In the 1960s he rejected that after the rise of the New Left.
In the 1970s he completed his move across the political spectrum by joining the Republican Party, which he said had once been as "foreign to me as attending a Catholic Mass".
Writing in 2003, Mr Kristol described neoconservatism as a "persuasion" and underlined that it had its roots among "disillusioned liberal intellectuals in the 1970s".
He also once famously described neoconservatives as liberals "mugged by reality".
The term neoconservatism was created by the socialist writer Michael Harrington in the early 1970s.
Fellow neoconservative founder Norman Podhoretz wrote that "the influence of Irving Kristol's ideas has been one of the most important factors in reshaping the American climate of opinion over the past 40 years".
Mr Kristol was a driving force in a series of think-tanks like the American Enterprise Institute that made conservatism a reigning ideology for at least two decades.
He wrote for many media outlets and penned several books including "Neoconservatism: The Autobiography of an Idea".
Former US President George W Bush, whose administration included several neoconservatives, issued a statement calling him "an intellectual pioneer who advanced the conservative movement".
But the reputation of the group was hit by controversy over the Iraq war in 2003 - which many neocons pushed for - and by the global economic downturn.
Mr Kristol did not comment much in public on the war.
With the election of Barack Obama, Mr Kristol's son William said that the liberals had regained the ascendancy.
"All good things must come to an end. Jan 20, 2009, marked the end of the conservative era," he wrote in the New York Times.
Irving Kristol married critic-historian Gertrude Himmelfarb in 1942. As well as his son William, he had a daughter Elizabeth.