David Koch Is Retiring From Koch Industries, Political Network

June 5, 2018, 2:35 PM UTC

David Koch, the billionaire businessman who has had a profound impact on the national political scene, is stepping away from the empire he created with his brother.

Citing health reasons, Koch will retire from Koch Industries and the board of the Americans for Prosperity Foundation, according to an internal memo cited by CNBC. Along with his brother Charles, David Koch has helped lead the rise of the Tea Party, which some say opened the door for Donald Trump’s ascension to the presidency.

Koch reportedly was diagnosed with prostate cancer more than 20 years ago. He and his family have donated millions to fight the disease, along with other philanthropic efforts. He and Charles preferred to stay in the political shadows, but were forced into the spotlight in 2010 after a piece in The New Yorker detailed their fight against Obama policies, including the Affordable Care Act.

“Due to health reasons, David Koch will be resigning from the board of Americans for Prosperity Foundation,” Mark Holden, co-chairman of the Koch-backed Seminar Network, said in the memo obtained by CNBC. “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. We wish him and his family well.”

This year, the Kochs are expected to spend $20 million on media buys extolling the benefits of recent tax legislation, to assist Republicans in their effort to keep control of the House and Senate. (They spent another $20 million to advocate for its passage.) The Koch political network is expected to spend between $300 million and $400 million in 2017-2018.

David Koch’s political power might be his ultimate legacy, but he and Charles have also built a powerhouse business in Koch Industries. Among its holdings are Stainmaster Carpet, Lycra, Quilted Norther toilet paper and Dixie Cups.

The Kochs were also financial backers of Meredith’s recent purchase of Time Inc. Meredith is the owner of Fortune.

Subscribe to Well Adjusted, our newsletter full of simple strategies to work smarter and live better, from the Fortune Well team. Sign up today.