David had reportedly been in declining health since at least 2018

David Koch, a billionaire industrialist, philanthropist and patron of numerous conservative and libertarian political causes along with older brother Charles Koch, has died. He was 79.

His death on Friday morning was announced by Koch Industries later that day. The company’s obituary for him noted that he had “many years of fighting various illnesses.”

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David, who this year had assets worth nearly $50 billion, according to The New York Times, was in declining health since at least 2018. That June, the eponymous company he had for years run with his brother announced he would be retiring from public life, according to CNN.

He had been hospitalized in 2016, according to NPR, and his “health has continued to deteriorate,” Charles wrote in a letter to Koch Industries employees last year, CNN reported.

“As a result, he is unable to be involved in business and other organizational activities. Because of this, David will be retiring from his responsibilities at Koch and other organizations,” Charles wrote.

David was previously diagnosed with prostate cancer in the ’90s, NPR reported, though further details of his health at his retirement were not released.

Leaders of one of the nation’s largest privately held firms, the Koch brothers — as they were most commonly known — spent liberally to support their various political pursuits, according to reporting on their donations.

Causes reportedly included pushing back on policy to combat climate change — oil and gas are major parts of the Koch business — as well as pushing to decrease taxation and opposing President Barack Obama‘s signature Affordable Care Act.

Their immense wealth and unabashed blending of money and politics made them major targets of criticism in more recent years, largely from Democrats who described the Koch brothers as puppeteers of democracy.

“What is un-American is when shadowy billionaires pour unlimited money into our democracy to rig the system to benefit themselves and the wealthiest one percent… the Koch brothers seem to believe in an America where the system is rigged to benefit the very wealthy,” then-Senate Majority Leader Harry Reid said in 2014, according to NPR.

Image zoom David Koch (left) in 2017 Owen Hoffmann/Patrick McMullan via Getty

Image zoom David Koch in 1989 Michel Delsol/Getty

Image zoom David Koch (second from right) in 2014 Paul Zimmerman/WireImage

Image zoom David Koch (center) in 2011 Chip Somodevilla/Getty

The Kochs, though reliable Republican backers, had a set of more idiosyncratic beliefs that over time placed them at odds with mainstream conservatism.

Their political network, from which David retired along with his other duties in 2018, also supported pro-trade and pro-immigration causes — in contrast to President Donald Trump‘s positions on both.

In 1980, David ran for the vice presidency on the Libertarian ticket.

In the obituary published by Koch Industries, Charles recalled his younger brother as having an “insatiable thirst for knowledge” — just like their father.

“It is what caused him to be one of the best I’ve ever seen at combining commercial and technical ability,” Charles said in 2007, according to the obituary.