New York City has long been the world's leading city for the uber-wealthy. It's easy to see why, with iconic cultural and business hubs such as Wall Street and Fifth Avenue.
Recently, however, several other international cities have challenged New York's claim as the top playground for the world's super-rich. According to the annual Knight Frank's Wealth Report, New York City fell from first place all the way to fourth in a list of cities most populated by those with more than $30 million in personal wealth; it now trails London, Tokyo and Singapore.
New York City remains home to the most billionaires, however, with 78 qualifying individual residents (according to Forbes magazine's 2015 billionaire list). That's 10 more than the second biggest billionaire population in Moscow and 32 more than fourth-place London. New York City's billionaires come from diverse business backgrounds, including a controversial former mayor who has been a Democratic, Republican and independent politician.
1. David Koch ($41 Billion Net Worth)
Depending on the list, David Koch is somewhere between the fourth and eighth wealthiest person in the world, usually tied with older brother Charles, who lives in Wichita, Kansas. A trained chemical engineer with a master's degree from MIT – where he was also a star basketball player – Koch is widely considered one of the most influential figures in America.
By the time Koch joined the family business, Koch Industries, in 1970, it was already a powerful enterprise. Under the stewardship of executive vice president David and chief executive officer (CEO) Charles, however, the oil and refining company transformed into an international conglomerate and is currently the second-largest privately held company in the United States, after Cargill. Koch Industries has operations in oil pipelines, domestic household items, building materials, finance, ranching and many other industries.
A leading philanthropist, Koch has donated more than $1.2 billion to charity over the course of his professional life. He is also a libertarian activist and serves on the board of the Aspen Institute, the Cato Institute, the Reason Foundation, the Americans for Prosperity Foundation and even ran for vice president on the Libertarian Party ticket in 1980.
2. Michael Bloomberg ($38.6 Billion Net Worth)
Michael Bloomberg is the richest politician in modern American history. He is the founder and CEO of Bloomberg, L.P., an international financial media company, and he eventually succeeded Rudy Giuliani as mayor of New York City in 2002. There are constant rumors that Bloomberg, now a registered Independent, has aspirations for the White House.
Bloomberg began his career in finance after graduating from Harvard Business School in 1966. By 1973, he was a general partner at the investment bank Salomon Brothers. He left Salomon Brothers in 1981 with a multimillion-dollar severance package and subsequently founded Innovative Market Systems, which was eventually renamed Bloomberg L.P. The company is widely credited for modernizing financial trading with the Bloomberg Terminal system.
As mayor, Bloomberg created controversy when he challenged and changed the city's term limit laws to run for a third consecutive term in 2009; he eventually won and served a third term until 2013. Bloomberg has given more than $3.5 billion to charity, including $100 million to the New York technology campus for Cornell University in 2015.
3. Carl Icahn ($20.5 Billion Net Worth)
Carl Icahn is on the short list of the most successful investors of all time, perhaps just below Warren Buffett and George Soros. Icahn serves as a hedge fund manager for Icahn Capital Management, and he is the founder and majority shareholder of Icahn Enterprises.
Icahn cut his investing teeth in the 1960s, focusing on options trading and arbitrage. By the 1970s, he started purchasing controlling interests of promising companies, including RJR Nabisco, Texaco, Western Union, Viacom, Marvel Comics, Blockbuster, Time Warner, Netflix and Motorola. When asked about his philosophy, he has responded that "generally – with exceptions – I buy something when no one wants it." He remains one of the most high-profile contrarian investors in the world.