Billionaire and major donor to the Republican party David Koch has died aged 79, Koch Industries confirmed on Friday.
The former majority owner of Koch Industries, alongside his brother Charles Koch were estimated to be worth $US50.6 billion ($71.3 billion) each.
Forbes ranking them as the 11th richest men in the world last year.
“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,” Charles Koch wrote in a statement on the company’s website.
He said that his brother had been diagnosed with prostate cancer 27 years ago.
“David liked to say that a combination of brilliant doctors, state-of-the-art medications and his own stubbornness kept the cancer at bay,” Mr Koch wrote.
“We can all be grateful that it did, because he was able to touch so many more lives as a result.”
The company founded by the Koch brothers is the second largest privately owned business in the US, which has interests ranging from pipelines to paper towels.
Philanthropist and patron of cultural and medical institutions, Mr Koch amassed his vast wealth with a large ownership stake in Koch Industries, the Wichita, Kansas-based company he ran with Charles.
With Charles as chairman and chief executive and David as executive vice president, Koch Industries aggressively expanded beyond the oil refining business their father created into an array of new ventures.
Together, the Koch brothers were regarded among the most influential conservative donors in the US.
The brothers, despised by liberal Americans, previously funded groups denying climate change and attacking unions and worker’s rights.
They also founded the anti-tax, small government group Americans for Prosperity.
In June 2018, Mr Koch retired from his roles at Koch Industries, citing his declining health.
Mr Koch is survived by his wife Julia Flesher Koch and his children Mary, John and David.