One of the best-kept secrets in American philanthropy is a group of three men with philanthropic assets totaling more than $13 billion who for years have been giving in almost complete anonymity to causes such as human rights, medical research, and the environment, Bloomberg Businessweek reports.

Since the 1990s, Andrew Shechtel, David Gelbaum, and C. Frederick Taylor, partners in a hedge fund called TGS Management, have been giving large sums of money away in near-total secrecy through a variety of anonymous vehicles, including the Gabriel Trust and Endurance Funding Trust, which together have assets valued at about $9.7 billion; only the Gates, Ford, and Getty foundations have more. Indeed, since 2000 a dozen anonymous private foundations funded and controlled by limited liability companies connected to the three men have distributed more than $1.8 billion to charity or charitable vehicles, including more than $700 million for Huntington's disease research and $1 billion to donor-advised funds like the Vanguard Charitable Endowment Program. The causes supported by the three men have ranged from the Sierra Club, to the conservative Hudson Institute, to a program run by the liberal Project Vote founder Sanford Newman.

The sources of the funds controlled by the three are hidden behind layers of company subsidiaries. Registered in Utah, the Gabriel and Endurance Funding trusts are controlled by companies in Nevada and Wyoming, which use the addresses of local law firms and, in turn, are controlled by other entities in Delaware. Using intermediaries to disguise a private foundation's backers is extremely unusual, Gregory Colvin, a lawyer who has practiced nonprofit law for decades, told Businessweek. It is contrary to the spirit, though probably not the letter, of private foundation rules, Colvin added. "Most of us who practice in the tax-exempt arena would regard setting up a private foundation as a full-disclosure vehicle."

The byzantine nature of those arrangements has enabled Shechtel, Taylor, and Gelbaum to avoid almost all public scrutiny of their activities. Within a few years of founding TGS, Businessweek reports, the three math whizzes had made enough to close the fund to new investors. With no need to solicit additional funds, the partners found it easy to keep their investment strategies secret and maintain a low profile. Taylor, together with two of his brothers, also created a consulting firm for anonymous donors that, according to its Web site, "coordinates grantmaking programs that advance the realization of human rights and social and economic justice for all people."

A predilection for secrecy has not kept TGS from lobbying Congress to provide more generous tax breaks for donors who target rare diseases or contribute securities to a private foundation. And in one exception to his policy of giving anonymously, Taylor helped his son Joshua set up 9 Dots, an afterschool program that provides middle-school students in a poor Los Angeles neighborhood with access to computers and science instruction.

"That's where the best opportunities of the twenty-first century are — if kids don't get exposure to STEM, they can't take advantage of those opportunities," said Joshua Taylor. "I think everyone deserves a shot."