Billionaire conservative donor David Koch has died at age 79.
Along with his brother Charles, David Koch donated hundreds of millions to conservative organizations over the course of his lifetime.
He was also known for his non-political philanthropy. Koch gave millions of dollars to the American Museum of Natural History in New York and served on its board for 23 years. He also donated $60 million to the Metropolitan Museum of Art in New York in 2012.
He was also a supporter of cancer research since being diagnosed with prostate cancer in 1992, making donations to Johns Hopkins, the Memorial Sloan Kettering Cancer Center, and his alma mater, MIT.
Koch was worth an estimated $58.7 billion when he died, per Bloomberg's most recent report.
According to Bloomberg, most of Koch's wealth stemmed from his 42% stake in Koch Industries, the industrial conglomerate with an annual revenue of about $110 billion.
Koch retired from the company in June 2018 due to health reasons.
Koch primarily lived with his wife in New York City, but he also owned hundreds of millions' worth of real estate in New York, Colorado, and Florida.
According to calculations by Business Insider, Koch's real-estate holdings are worth at least $143 million (based on sale prices and Zillow estimates).
For 15 years, Koch lived in a massive 18-room duplex in a ritzy Manhattan building that John D. Rockefeller, Blackstone founder Stephen Schwarzman, and other business magnates have called home.
Koch paid $18 million for the duplex at 740 Park Avenue in 2004, according to The Real Deal.
740 Park Avenue is notoriously exclusive and expensive, known for being home to some of New York City's wealthiest residents.
To live at the Art Deco co-op, which opened in the 1930s, applicants reportedly must be able to show a liquid net worth of at least $100 million, as Business Insider previously reported in 2017.
As of 2017, maintenance fees could run up to $10,000 a month. And in 1990, 740 Park Avenue residents paid an average of $250,000 each to repair the building's facade, according to the 2006 book, "740 Park: The Story Of The World's Richest Apartment Building" by Michael Gross.
There are two condos currently for sale in the Park Avenue co-op, according to StreetEasy.
A five-bedroom unit is on the market for $29.5 million, and a three-bedroom penthouse is listed for $34.5 million.
In addition to his Park Avenue duplex, Koch owned a $40.25 million Manhattan townhouse. Sources told the New York Post in August 2018 that he and his wife paid cash for the property.
Koch bought the 15,000-square-foot mansion from real-estate developer Joseph Chetrit, according to the New York Post.
The eight-bedroom Upper East Side home, which was originally listed for $51 million, includes a 1,500-square-foot master suite, a gym, and a rooftop terrace.
Then there's Koch's oceanfront mansion on "Billionaire Lane" in the Hamptons, the ritzy vacation destination for New York City's wealthy elite.
Koch's seven-bedroom Southampton home, which includes a tennis court and outdoor swimming pool, has an estimated value of $18.8 million, according to Zillow.
In 2012, Koch hosted a $50,000-a-head fundraising dinner at his Hamptons home for then-presidential candidate Mitt Romney; the event was crashed by Occupy protesters.
Koch's Hamptons street, Meadow Lane, was nicknamed "Billionaire Lane" for its ultra-wealthy residents, who have reportedly included investor David Och, real estate mogul Aby Rosen, fashion designer Calvin Klein, and hotelier Ian Schrager.
According to Pitkin County property records, Koch also purchased two neighboring homes in Aspen, the upscale Colorado ski town.
Property records for the county show that Koch bought his first Aspen house for $1.9 million in 1989. Two years later, in 1991, he paid $1.75 million for another home on the same street.
Today, the first home has an estimated value of almost $18 million, and the second is valued at $8.8 million, according to Zillow.
Koch also had a 30,000-square-foot mansion in Palm Beach, Florida, called the Villa el Sarmiento.
Koch paid $10.5 million for the home in 1998, and he and his wife reportedly spent $12 million renovating and expanding it, bringing its size to 30,000 square feet.
Today, the mansion has an estimated value of more than $40 million.
