Billionaire businessman David Koch, one of the richest men in the world and a prominent Republican party donor, has died.
The co-owner of oil and manufacturing company Koch Industries, the second-largest privately held company in the US, is one of the world's most well-known businessmen and philanthropists.
He is reportedly the fourth richest person in the US and the wealthiest resident of New York City, reports News.com.au.
He and his older brother Charles, 83, have been among the biggest donors to the Republican Party since the 1980s.
"It is with a heavy heart that I announce the passing of my brother David," Charles Koch said in a statement. "Anyone who worked with David surely experienced his giant personality and passion for life."
He was the 1980 candidate for US vice president from the United States Libertarian Party, with Ed Clark the presidential candidate.
In 1984 he broke with the Libertarian Party when it supported eliminating all taxes. Since then, Koch has been a Republican.
Koch (pronounced coke) considered himself a social liberal, who supported a women's right to choose, gay rights, same-sex marriage and stem-cell research. However, he helped fund the conservative Tea Party wing of the Republican Party and has been called a climate change denier.
While he donated to the Republican Party he was not a fan of Donald Trump's. Their political network famously refused to endorse a candidate in the 2016 presidential election.
Trump once called the Koch brothers "a total joke in real Republican circles."
"I never sought their support because I don't need their money or bad ideas," he tweeted.
Koch, who stepped down from his role as executive vice president at the family's company over health concerns in July 2018, had a net worth of $US42.9 billion ($A63 billion), according to Forbes.
Koch married Julia Flesher in 1996. He has three children.
Flesher and his children put out a statement referring to him as their "walking Google."
"While we mourn the loss of our hero, we remember his iconic laughter, insatiable curiosity, and gentle heart," the statement said. "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. We will miss the fifth link in our family."
The New York State Theatre at Lincoln Centre, home of the New York City Ballet, was renamed the David H. Koch Theatre in 2008 after a gift of $US100 million ($A148 million) for the renovation of the theatre.
The circumstances surrounding his death weren't immediately clear. He was diagnosed with prostate cancer in 1992 and given five months to live. He says his battle with cancer prompted him to give millions to medical research.
"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 read. "We can all be grateful that it did, because he was able to touch so many more lives as a result."
Koch survived another brush with death as a passenger of USAir Flight 1493, when it collided with another aircraft on a runway at Los Angeles International Airport in February 1991. In total, 33 people were killed in the disaster.
"I was amazed that I had survived this accident. Looking back on it I felt that the good Lord was sitting on my shoulder and that he helped save my life because he wanted me to do good works and be a good citizen. Following that revelation I became tremendously philanthropic," he told Barbara Walters.
Koch and his twin brother Bill were born in Wichita, Kansas, in May 1940.
He earned a bachelor's and a master's degree in chemical engineering from the esteemed Massachusetts Institute of Technology.
He joined Koch Industries, the company founded by his father, in 1970 as a technical-services manager.
He and his brother, Charles each owned 42 per cent of Koch Industries after buying out the shares of their brothers Bill and Frederick for $US1.1 billion. That came after Bill and Frederick tried to oust Charles as CEO and they tried to sue Charles and David. Their mother Mary said she would disinherit any brother who tried to sue any of their siblings.