It’s also worth noting that the hedge fund billionaire is an almost uniquely American species. Mr. Vardi said that Forbes had found no such billionaires in Asia, for example. The only other place where they flourish is in London, and that may change if Europe’s financial center shifts away from England after it voted last year to leave the European Union.

Not surprisingly, the decline in hedge fund managers among the richest Americans parallels a drop in the number of hedge funds operating. Back in 2005, for example, 2,073 new hedge funds opened their doors.

Now, many of these funds are closing. According to the research firm HFR, during the first three quarters of 2016, hedge fund liquidations totaled 782, on track for the highest number since the 2008 financial crisis. The number of new hedge funds was also down in the period.

All told, the number of hedge funds peaked in 2014 at 10,142. Today, the figure stands at 9,925, HFR said.

“By and large, this is a group that comes and goes,” said John C. Bogle, founder of the Vanguard Group and creator of the first stock index fund. “These are brilliant men and women. They’re over my head in depth of knowledge, but on average, they are going to all be average.” In other words, these managers cannot beat the market forever, and their performance will eventually revert to the mean.

Even as the number of hedge funds has fallen, the assets they have under management have stayed aloft. This is largely because of the recent run-up in stock prices. Hedge fund assets approached $3 trillion in the third quarter of 2016, according to HFR, up from around $1.5 trillion in 2006.

Given the trillions of dollars under management, it’s easy to see how the business could create such riches among its overseers. Indeed, charging investors 2 percent in management fees every year and 20 percent of the profits earned, hedge fund managers have one of the better get-rich-quick schemes ever devised on Wall Street.