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 on 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. He is survived by his wife Julia and their three children.

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 rivalled the spending and scope of the national Republican Party, and analysts view their activism as helping to have fuelled the Tea Party movement.

Koch’s death is not expected to bring major changes to the network founded by Charles Koch and now overseen on a day-to-day basis by his top lieutenant Brian Hooks.

The organization already was in midst of transformation when David Koch stepped away from his formal roles. The Koch groups now are called Stand Together and have made more investments in philanthropy and policy issues, such as K-12 education.

David Koch was most active in Americans for Prosperity, the grass-roots 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 percent of the vote.

The Koch network has spread a hardline, limited-government message that has helped move the GOP to the right in recent years, as they bankrolled efforts to elect conservatives to Congress and statehouses around the country.

Their activism made them villains to Democrats; then-Senate Majority Leader Harry Reid, a Nevada Democrat, once denounced them as “power-drunk billionaires” out “to buy the country.” But it also put them at odds with Trump, who called them a “total joke” last year after Charles Koch and his top lieutenants publicly criticized the administration’s trade policies.

Even so, the Kochs have close ties to key figures in the administration, including Vice President Mike Pence and Secretary of State Mike Pompeo, who represented Wichita in the US House.

Pompeo on Friday tweeted his condolences, calling David Koch “a compassionate philanthropist, successful businessman, and a proud American.”

The two brothers largely made their fortune through Koch Industries, 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. In March, Forbes listed both Koch brothers as the 11th wealthiest men in the world, with an estimated individual worth of $50.5 billion.

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.