Conservative billionaire David Koch, who became a household name through the policy and political empire he created with his older brother, Charles, has died. He was 79.

Charles Koch, the CEO of the family’s industrial conglomerate Koch Industries, announced the death Friday.

“It is with a heavy heart that I announce the passing of my brother David. Anyone who worked with David surely experienced his giant personality and passion for life,” the elder Koch said in a statement. The statement did not cite a cause of death but noted David Koch’s decades-old battle with prostate cancer.

Koch retired from the company and the Koch political operations in 2018, citing health reasons. Sources close to the family told CNN he had been in declining health in recent weeks.

The Koch brothers were best known — and vilified by Democrats — for their role in politics, and they used their vast wealth to build a sprawling array of think tanks, foundations and political groups to spread their small-government, free-market message. In some elections, the Koch network rivaled the spending and scope of the national Republican Party, and analysts view their activism as helping to have fueled the Tea Party movement.

David Koch was most active in Americans for Prosperity, the grassroots arm of the Koch’s sprawling network, which built a coalition of more than 3 million activists to push the agenda of the Kochs and the roughly 700 like-minded donors to help fund their public policy work.

But in the era of President Donald Trump — whom Charles Koch pointedly declined to support in 2016 — the network has undergone a significant shift in focus, upping its commitment to work across party lines on top priorities, such as promoting free trade and creating a path to permanent legal status for undocumented immigrants brought to the US as young children.

In June, Americans for Prosperity announced four new political action committees and said it would wade into primaries to help incumbent politicians, including Democrats, who side with Koch on trade, immigration and other issues.

David Koch himself entered politics decades ago, waging an unsuccessful bid as the Libertarian Party’s vice presidential nominee in 1980 with Ed Clark. They won just 1% of the vote.

One of the world’s richest men

In March, Forbes listed both Koch brothers as the 11th wealthiest men in the world, with an estimated individual worth of $50.5 billion. The two brothers largely made their fortune through Koch Industries, which they inherited from their father. An industrial conglomerate and one of the world’s largest private companies, the company is engaged in everything from oil refining to making consumer products such as Brawny paper towels.

As philanthropists, the brothers’ mission expanded to include large donations to colleges and universities as well as advocating for criminal justice reform. They also dedicated funds toward medical research and the arts.

David Koch, a well-known figure in New York, became a major benefactor of the Memorial Sloan Kettering Cancer Center and a patron to arts organizations. A dance-focused theater at Lincoln Center bears his name, courtesy of his $100 million pledge in 2008. Last year, Koch Industries said David Koch’s donations and pledges to philanthropic organizations had topped $1.3 billion.

“Twenty-seven years ago, David was diagnosed with advanced prostate cancer and given a grim prognosis of a few years to live,” Charles Koch said in Friday’s statement. “David liked to say that a combination of brilliant doctors, state-of-the-art medications and his own stubbornness kept the cancer at bay. We can all be grateful that it did, because he was able to touch so many more lives as a result.”

This story is breaking and will be updated.

David Koch, billionaire businessman and influential donor, dies