The 78-year-old cited health reasons in a letter distributed to company officials on Tuesday morning.
David Koch, the billionaire industrialist who has donated countless millions to conservative causes, plans to retire from his leadership roles at Koch Industries and the so-called Koch network of wealthy right-leaning donors.
Mark Holden, who has spent a career at Koch Industries and now helps run their political efforts, said in an email the Koch network will continue to expand even as one of its founders steps aside.
Democrats have demonized the Koch brothers for their outsized influence in conservative politics over the last decade.
David and Charles Koch are widely known for their financial support of conservative causes that favor businesses and stricter environmental regulation, according to the New York Times. The longtime philanthropist, who has supported vaunted NY institutions such as the American Museum of Natural History, the Metropolitan Museum of Art and the Lincoln Center, also funded a cancer research institute at MIT and has donated over $700 million to medical causes since his 1992 cancer diagnosis.
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The news comes a day after the brothers said they will launch a multimillion-dollar campaign to oppose President Donald Trump's tariffs, and to champion free trade.
David Koch had served as an executive vice president and a board member of Koch Industries, a Wichita, Kansas-based conglomerate with interests ranging from oil and ranching to farming and the manufacturing of electrical components.
As Koch Industries' profile rose, so did David Koch's involvement in politics and philanthropy.
During the 2016 presidential campaign, the Kochs kept their distance from Trump.
David ran as a Libertarian candidate for president in 1980, and together the Koch brothers made large contributions to the Republican Party in 2010, facilitating the party's rise in the House of Representatives in that year's elections. "We greatly appreciate his vital role on the board and all that he has done to help us build a strong foundation for our future success".
Although David Koch's involvement had been reduced in recent years, he still held several top positions within the Koch network, including as chairman of a foundation that supports Americans for Prosperity.
David Koch, along with his brother Charles, owns the second largest private US company, whose operations range from refining and chemicals to ranching and forest products.