OVER the past year, the main story line in the push for marriage equality has been the ardor and success with which leading Democratic politicians have taken up the fight. The Democratic governors of New York, Maryland and Washington all promoted and signed same-sex marriage laws, for which President Obama expressed his support last month.

But the progress within Republican ranks has also been pivotal, not to mention fascinating. And a compelling character in that subplot just added a new twist to the narrative, one that suggests the rapidly changing political dynamics of this issue and its potential import to a party dogged by an image of being culturally out of touch.

That character is Paul E. Singer, 67, a billionaire hedge fund manager who is among the most important Republican donors nationwide. In just one Manhattan fund-raiser last month, he helped to collect more than $5 million for Mitt Romney’s presidential campaign.

He steadfastly supports conservative candidates. He also steadfastly supports gay rights in general and marriage equality in particular. Along with a few other leading Wall Street financiers, he contributed and helped drum up the majority of the money — more than $1 million — that fueled the campaign for same-sex marriage in New York.