US billionaire businessman and key Republican Party donor David Koch has died at the age of 79.

Koch stepped down from the family business, Koch Industries, last year amid health problems. His death has been confirmed by his older brother Charles.

“It is with a heavy heart that I announce the passing of my brother David,” says Charles Koch in statement. — Steve Herman (@W7VOA) August 23, 2019

David was listed by Forbes as the 11th richest billionaire in 2019. The family firm, launched by his father Fred, is the second-largest privately held company in the US, with revenues of around $110 billion a year.

Despite his conservative political connections, Koch held a variety of liberal positions, including being pro-choice and pro-gay marriage, and was staunchly opposed to both the drug war and US foreign intervention.

“I’m basically a libertarian, and I’m a conservative on economic matters, and I’m a social liberal,” Koch said in a 2014 interview.

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He supported a number of political think tanks including the now-defunct Citizens for a Sound Economy group, which he founded with his brother in 1984. He was also a donor to the Americans for Prosperity foundation, a major conservative lobbyist group, which the brothers founded in 2004.

Despite allegations to the contrary, David Koch denied any affiliation with the Tea Party movement, but said he sympathized with it. He also sat on the board of the libertarian Cato Institute and the Reason Foundation.

Together with his brother Charles, Koch made significant political contributions to leading figures in the Republican party, including to Wisconsin Governor Scott Walker’s 2010 election campaign and to Mitt Romney’s 2016 presidential campaign, though the brothers refused to donate to Donald Trump’s 2016 run.

The brothers reportedly pledged $60 million to defeat President Barack Obama’s re-election campaign in 2012.

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