Billionaire David Koch, a major donor to the Republican party, has died aged 79. He had been suffering from cancer.
The former majority owner of Koch Industries was ranked by Forbes, jointly with brother Charles, as the 11th richest person in the world.
Koch wielded huge political influence, bankrolling conservative causes for small government, low regulation and climate change scepticism.
He was also a major donor to medical research, education and the arts.
The brothers' political network funnelled hundreds of millions of dollars to Republican candidate Mitt Romney's failed presidential bid in 2012, only to fall out with President Donald Trump over his immigration policy and tariffs.
In 2018 Koch stepped down from Koch Industries - which refines crude oil, produces fertiliser, and manufactures household products - citing his declining health.
He had been a philanthropist to the arts, especially ballet, and donated to New York's Lincoln Center and Memorial Sloan Kettering Cancer Center hospital.
He ran for vice-president as a Libertarian in 1980, calling for the abolishment of many federal government agencies.
According to Forbes, he is estimated to be worth $42.4bn (£34.7bn).
The news of his death was confirmed in a statement from Charles Koch, who said that his brother was first diagnosed with prostate cancer 27 years ago and given only a few years to live.
"David liked to say that a combination of brilliant doctors, state-of-the-art medications and his own stubbornness kept the cancer at bay," Charles Koch wrote, adding that in those years he married his wife Julia Flesher and had three children.
He also described David as having a "giant personality and passion for life" and noted his "institution changing philanthropic commitments to hospitals, cancer research, education and the arts".
'Pushed Republicans to the right'
Analysis by Tara McKelvey, White House reporter
David Koch, who was born in Wichita, once said: "Hell, everybody from Kansas is a Republican."
In fact, there are plenty of Democrats in Kansas. But he was right about this - conservatism permeates the state. Kansas is a place where people believe in the individual spirit, free trade and free markets - and like to rail against Washington.
A libertarian, Koch fostered his economic ideas on a national level through organisations such as Americans for Prosperity, a right-wing advocacy group.
Over several decades, he helped to reshape conservatism in the US, pushing the Republican party to the right and inspiring leaders of the Tea Party movement who eventually helped to elect Trump.
A wealthy man who invested in both science (a dinosaur gallery at the American Museum of Natural History is named after him) and in libertarian, Kansas-bred economic ideas, Koch has had a profound impact on conservative thought in this country.
The company founded by Charles and David Koch - the second largest privately owned business in the US - has interests ranging from pipelines to paper towels.
According to the Koch Industries website, they have more than 120,000 employees between all their businesses and subsidiaries.
They have previously put money into groups denying climate change and attacking unions and workers' rights.
The brothers' political clout made them bogeymen for many on the political left.
But the Kochs have also pushed for criminal justice reform and made large donations to the American Civil Liberties Union.