FILE PHOTO: Business magnate George Soros arrives to speak at the Open Russia Club in London, Britain June 20, 2016. REUTERS/Luke MacGregor/File Photo

NEW YORK (Reuters) - Investor George Soros has transferred about $18 billion, the majority of his estimated fortune, to his Open Society Foundations, making them the second largest philanthropic grant-making group in the United States, according to media reports on Tuesday.

The foundations already controlled billions of dollars, but Soros, 87, has in recent years increased the pace of transfers from his hedge fund-turned-family office, Soros Fund Management LLC, the Wall Street Journal and the New York Times reported earlier on Tuesday, citing Open Society officials.

Representatives for Open Society did not respond to requests for comment from Reuters.

Open Society works globally to “build vibrant and tolerant democracies” and has given away nearly $14 billion since inception in 1979, according to its website.

Hungarian-born Soros, who made a huge profit betting against an overvalued British pound in 1992, is a vocal supporter of liberal causes and was a large contributor to the fund-raising Super PAC group backing Democratic presidential nominee Hillary Clinton last year.

Soros early this year hired former UBS Group AG asset management executive Dawn Fitzpatrick to serve as the latest chief investment officer for New York-based Soros Fund Management, which also manages money for Open Society.

Only the Bill & Melinda Gates Foundation is now larger than Open Society among U.S. grant-making groups, with an endowment of about $40 billion.

Soros is worth an estimated $23 billion, according to Forbes.