A battle within the Republican Party over same-sex marriage is unfolding on two fronts, in public, and behind the scenes. In the latter case, one of the most influential players is a billionaire hedge fund manager largely unknown to those who don't work in finance or mix with political mega-donors.

That man is Paul E. Singer, who over the years has used his wealth to spur Republicans to support gay marriage laws. Now, Singer is expanding his reach with the creation of an advocacy group which aims to spend millions influencing the legislative debate over same-sex marriage across the country.

Singer, the 68-year-old founder of Elliott Management Corporation, is not a newcomer to the political battle over gay rights. He coaxed Republican state senators in New York to back a same-sex marriage law in 2011, offering financial cover against backlash stemming from their votes, helping raise six figures for each of them.

The public side of the intra-party debate over gay marriage was visible when Sens. Rob Portman (R-Ohio) and Mark Kirk (R-Ill.) declared support for same-sex marriage, setting off a renewed debate about the issue in the GOP. And when the Republican National Committee recently reaffirmed its opposition to gay marriage, it also was plain to see.

Behind the scenes, donors are influencing the debate more quietly. On this second front, it is all about money and organization. And for Singer, it’s about being there financially for Republicans who decide to back same-sex marriage.

Singer declined to be interviewed for this story, but agreed to answer questions via e-mail. He sees donors and politicians, he said, as “complementary forces,” and is signaling to elected officials they will have backup if they decide to support same-sex marriage.

“We are heartened to see many politicians in both parties moving in the right direction on this,” he wrote. “Our job is to let them know they have plenty of like-minded friends, activists and party leaders who will stand with them.”

For Singer, there is a personal connection to the issue. His son is gay, and got married in Massachusetts, something Singer mentioned in a 2010 speech at a fundraiser for the American Foundation for Equal Rights.

Singer started American Unity PAC in 2012, infusing the operation with a big early donation. The super PAC spent over $2 million on congressional races last cycle, according to data compiled by the Center For Responsive Politics. The group had limited success, backing more losing candidates that winning ones.

Even so, the creation of the PAC offered a new financial vessel for donors looking to protect Republicans friendly to gay rights, serving as a countermeasure to anti-gay marriage groups like the National Organization For Marriage.

Several months ago, Singer laid the groundwork for American Unity Fund, an 501(c)(4) nonprofit affiliated with the super PAC. The effort was officially announced last week. It's an effort to branch into advocacy and lobbying, and to delve further into legislative battles at the state level.

American Unity Fund has already raised $2 million and plans to raise millions more. It recently found success in Rhode Island, which on Thursday became the 10th state to legalize gay marriage. The group convinced state senate Republicans to support gay marriage there and is also trying to win over Republican lawmakers in Minnesota, where there is a legislative effort to legalize same-sex marriage.

There’s a “sentiment among leading center-right donors that it is important to make a compelling and honest case with why the freedom to marry is consistent with conservative values,” said American Unity Fund spokesman Jeff Cook-McCormac.

Singer has also donated big money over the years to other Republican causes and candidates. He believes supporting gay marriage is wholly consistent with conservatism. He argues for individual freedom when he makes his case. "I believe marriage equality is critical to the future of individual liberty and the strength of the American family, and the Republican Party should stand for both,” said Singer.

But there are many conservatives who aren’t convinced. One need look no further than Portman’s announcement that he supports gay marriage. The news prompted some social conservatives to reaffirm their commitment to marriage as strictly between one man and one woman.

And even as Americans have moved sharply toward favoring same-sex marriage during the last decade, most Republicans remain opposed, polling shows. According to a recent Washington Post-ABC News survey, even as the percentage of Republicans who say gay marriage should not be legal has dropped since 2004, most still oppose it.

For Singer, it’s a project that advances in increments. He said he believes that evidence in the states where gay marriage is legal should help convince more conservatives to support it.

“Ultimately, this fight is about basic equality and individual liberty -- both conservative principles,” Singer concluded in his e-mail. “But for those who remain unconvinced, state-by-state evidence that marriage equality does no harm and actually strengthens families and the institution of marriage should put doubts to rest and pave the way for more conservatives to join this growing movement.”