Along with gold, General Motors and Apple rank among his biggest long positions, both of which have had uneven returns in recent months. His fund has held a small position in Greek bank stocks and warrants. “Greece has been anything but sun-kissed,” Mr. Einhorn wrote in his July letter.

Adam Taback, president of alternative strategies for Wells Fargo Private Bank, said, “I don’t think he got any dumber — he’s one of the brightest guys in the industry. I don’t think he’s lost his edge. I think he’s just had a bad run.” Mr. Taback pointed to the Federal Reserve’s quantitative easing — pumping money into the financial system — as a factor that had made Mr. Einhorn’s job more difficult, because stocks tend to rise and fall together.

“If you look at the market, it isn’t pricing risk in the way it should be, and it’s very difficult to get things right,” Mr. Taback said.

Still, some investors speculated that Mr. Einhorn might be managing too much money and that his firm is not as nimble as it once was, making it more difficult to exit losing positions.

In the hedge fund industry, Mr. Einhorn has developed a reputation for accurately identifying stocks that will plunge in price and sectors that will be hit. Earlier this year, he announced that he was broadly shorting oil drillers and fracking companies, including Pioneer Natural Resources. With energy prices plummeting in August, his bet against much of the oil sector most likely helped minimize his firm’s losses. But the coal producer Consol Energy, another of his biggest positions, ended the month roughly flat.

Mr. Einhorn, who started his firm in 1996 with $1 million that was invested by family and friends, may be most famous for his 2008 presentation questioning the finances of Lehman Brothers, several months before the investment bank collapsed in the financial crisis. But not even Lehman’s failure could prevent a roughly 23 percent loss for the firm that year, a bleak time for many hedge funds.