In 2015, Dalio's $82 billion Bridgewater Pure Alpha fund generated $3.3 billion in net gains for investors, according to the report.

Meanwhile, Soros' $29 billion Quantum Endowment Fund, a family office hedge fund, dropped from the No. 1 spot on last year's list to No. 2.

Quauntum, which had been led in recent years by Soros' protege Scott Bessent, made $900,000,000 in net gains for 2015, the report said. Bessent just started his own hedge fund, Key Square Group, this month and will be managing nearly $4.5 billion in assets,

Another standout on the list is billionaire Steve Cohen, who now runs family-office Point72 Asset Management (formerly SAC Capital). He generated $1.7 billion in net gains in 2015 for himself and his employees.

Collectively, the top 20 fund managers made their investors $15 billion in net gains in what was an incredibly underwhelming year for hedge funds.

"The returns from hedge funds in 2015 overall was unsatisfactory, because they lost money for investors. However, once again, the top managers significantly outperformed the average hedge fund manager," said Rick Sopher, chairman of LCH Investments. 

Reuters/ Carlo AllegriJohn A. Paulson

However, not everyone on the list had winning years. Some, in fact, lost money. 

John Paulson, the founder of $18 billion Paulson & Co., fell in the ranks from No. 3 in 2014 to No. 7 in 2015. LCH estimated that his fund lost investors $2.1 billion in 2015.

Meanwhile, The Baupost Group, the Boston-based hedge fund led by Seth Klarman, held its No. 4 spot despite losing about $800,000,000 million, according to the LCH report. 

Baupost's

Newcomers to the list include Maverick Capital, led by "Tiger Cub" Lee Ainslie, and Lansdowne Developed Markets, comanaged by Peter Davies and Stuart Roden. Ainslie's fund made its investors $1.1 billion in 2015, while Lansdowne earned $2.1 billion.

"Lansdowne Developed Markets are the second European-based firm to enter the top 20; they have made $11.8 billion of gains for investors after fees since launch in 2001, partly from correctly and consistently anticipating the great changes in the business and financial landscape that have occurred in this period," Sopher said.

Last year, Ackman, then 48, was the youngest fund manager ever to make the list, debuting at No. 19. In 2015, Pershing Square had its "worst year" in the fund's history, falling 16.54%, according to data compiled by HSBC. The fund was down 12% for the year through January 19, HSBC's data showed.

Also, ESL Investments, the hedge fund led by Eddie Lampert, fell off the list this year.