David Koch, the billionaire conservative activist and philanthropist, who was lauded by the right and rebuked by the left, has died.
He was 79.
“It is with a heavy heart that I announce the passing of my brother David," Charles Koch said in a statement Friday. "Anyone who worked with David surely experienced his giant personality and passion for life."
Charles Koch did not say how his brother died, but David Koch blamed deteriorating health when he stepped down last year from Koch Industries, a Kansas-based energy and chemical corporation with an annual revenue of about $110 billion.
Download the NBC News app for breaking news and politics
David Koch, regarded as the more gregarious of the two brothers, served as the executive vice president of Koch Industries. He held a master's in chemical engineering from the Massachusetts Institute of Technology.
Charles Koch, who also has engineering degrees from MIT, is the company's chairman and chief executive officer.
The brothers were tied as 11th richest in the world this year in a ranking by Forbes. At the time of his death, David Koch was worth $42.4 billion.
David and Charles Koch, along with their brothers, Frederick and Bill, inherited the business when their father, who founded it, died in 1967. Frederick and Bill Koch sold their stake in 1983, and in 1998 pursued an unsuccessful lawsuit against the other two brothers, claiming they were cheated when they were bought out of the private company. David and Bill were twins.
With the wealth from their business, David and Charles Koch helped to build a massive conservative network of donors for organizations that work to mobilize voters and sway elected officials in support of libertarian-leaning economic policies.
Let our news meet your inbox. The news and stories that matters, delivered weekday mornings.
They founded the nonprofit Americans for Prosperity, which has spent more than $1 billion over the past several elections to support candidates who adhere to their free-market, small-government, libertarian ideals. While they distanced themselves from the movement, touting instead classic libertarian ideals, the brothers are also credited with helping to fuel the tea party.
While celebrated on the right, the Koch brothers are often regarded by Democrats as a symbol of the corrupting force of corporate money in American politics.
Koch money was used in fighting former President Barack Obama's health care initiatives and given to groups that deny climate change, undercut unions and oppose gun laws. It also contributed to the prominence and volume of issue-oriented political television ads.
But the Kochs had more recently split with the GOP under President Donald Trump — refraining from publicly endorsing him in 2016 and launching a multimillion-dollar campaign last year promoting free trade and warning against tariffs. Still, Trump's political rise is often partially attributed to their contributions to causes that championed the Trump agenda.
"David Koch lived long enough to see his dreams come true. Massive tax cuts for the rich, rampant environmental deregulation, America out of Paris accords," environmentalist and author Bill McKibben wrote on Twitter on Friday. "He got what he paid for."
David Koch himself ran as the Libertarian Party's vice presidential candidate in 1980. He and the party's presidential nominee, Ed Clark, won a little more than 1 percent of the vote.
"Today, our 1980 nominee for Vice President David Koch passed away. Often a focal point of political debate, David spent much of his life contributing and working in his own way toward what he believed in: a freer world," the Libertarian Party said in a statement Friday.
David Koch, who had survived prostate cancer, donated hundreds of millions of dollars to medical research.
"Memorial Sloan Kettering is tremendously grateful to David Koch and the legacy his leadership and generosity leaves for cancer research and treatment," said the New York cancer center's president and CEO Craig B. Thompson. "His profound commitment to cancer will live on through a state-of-the-art outpatient center named in his honor and opening later this year."
Koch was also a huge supporter of the arts, specifically in New York City where he lived. His donations included $65 million to support a renovation of the Metropolitan Museum of Art.
“David Koch was an unwavering supporter of our Museum, reflected in his service as a trustee and his most generous philanthropic support. We are extremely grateful for his generosity and send our condolences to Julia and his entire family," a statement from the Met said. The museum's front plaza, which is adorned with two massive fountains and stretches four blocks, is named for Koch.
The David H. Koch Theater at the Lincoln Center and the David H. Koch Dinosaur Wing at the American Museum of Natural History also got their names following contributions from him.
And a wing at the Smithsonian's National Museum of Natural History and MIT's Institute for Integrative Cancer Research were also named in his honor after multimillion-dollar donations.
When he was diagnosed with cancer 27 years ago, he was given five years to live, his brother said.
"David liked to say that a combination of brilliant doctors, state-of-the-art medications and his own stubbornness kept the cancer at bay," Charles Koch's statement said. "We can all be grateful that it did, because he was able to touch so many more lives as a result."
"The significance of David’s generosity is best captured in the words of Adam Smith, who wrote, ‘to indulge our benevolent affections, constitutes the perfection of human nature,'" Charles Koch said.
David Koch is also survived by his wife, Julia, and their three children.
“While we mourn the loss of our hero, we remember his iconic laughter, insatiable curiosity, and gentle heart," Julia Koch said in a statement.
"His stories of childhood adventures enlivened our family dinners; his endless knowledge rendered him our ‘walking Google.’ His sensitive heart had him shed a tear at the beauty of his daughter’s ballet, and beam with pride when his son beat him at chess," she wrote. "We will miss the fifth link in our family."