Billionaire conservative icon David Koch has died at age 79, his older brother Charles Koch said in a statement Friday. The New York resident was suffering from deteriorating health as of late, according to a letter Charles Koch sent last summer to officials with their company, Koch Industries.

Businessman David Koch arrives at the Metropolitan Museum of Art Costume Institute Gala Benefit in New York May 5, 2014. Reuters/Carlo Allegri

In his statement, Charles Koch said his brother was diagnosed with advanced prostate cancer more than two decades ago. "Anyone who worked with David surely experienced his giant personality and passion for life. Twenty-seven years ago, David was diagnosed with advanced prostate cancer and given a grim prognosis of a few years to live. 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," Charles Koch said.

Charles Koch said his brother would be "greatly missed, but never forgotten." David Koch had recently stepped down from the brothers' network of business and political activities.

They have long been involved in supporting the Republican Party and criticized by Democrats for their outsized influence in conservative politics. The brothers declined to spend anything on the last presidential race between Donald Trump and Hillary Clinton.

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David Koch was less involved in politics than his brother and more known for his philanthropy to education and the arts, particularly ballet. He gave $100 million to renovate the New York State Theater in Lincoln Center, which was renamed for him in 2008.

David Koch also committed millions to various hospitals for cancer research. Quoting the pioneer of political economy, Charles Koch said Friday 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.'"