On Wednesday, when the Supreme Court convenes to hear arguments in the second of two cases challenging the 1996 Defense of Marriage Act, the person who will stand front and center before the nine justices won’t be Edith Windsor, the vivacious 83-year-old widow whose name is on the case, but her lawyer, Roberta Kaplan, who will be fighting for federal government recognition not only of Windsor’s marriage to another woman, but of her own.Kaplan, known in legal circles as a powerhouse corporate litigator, is one of a handful of attorneys who over the past decade have decisively shaped and driven the legal fight for same-sex marriage nationally. She lost her first major case, a 2004 suit filed by 13 couples in New York State, including a woman awaiting a liver transplant who wanted to make sure her partner of 24 years could visit her in the hospital. But because the ruling said lawmakers should be the ones to decide if the laws should be changed, it paved the way for the 2011 vote in New York’s legislature legalizing same-sex marriages in the state. Now Kaplan is hoping to win what would be a landmark national court decision by arguing that the government shouldn’t hold Windsor, whose wife Thea Spyer died in 2009 after a decades-long struggle with multiple sclerosis, liable for $363,053 in federal estate taxes she never would have been asked to pay if she’d been married to a man.Kaplan was recruited by the ACLU to litigate the 2004 suit, which was filed after the mayor of New Paltz began issuing marriage licenses to same-sex couples, in part because she had clerked on New York State’s Court of Appeals, which eventually heard the case. Windsor came to Kaplan through a more traditional route: through mutual friends who were trying to help the new widow out of desperate financial straits.Windsor, a Temple University graduate from Philadelphia, met Spyer, who was born in Amsterdam but who fled the Holocaust with her family and eventually came to the United States as a refugee, at a Greenwich Village restaurant called Portofino in 1963, six years before the gay rights movement was born at the Stonewall Inn, a few blocks away. The pair danced all night and, in 1967, got engaged with a diamond brooch rather than a ring—a ruse to protect Windsor, a mathematics major and rising IBM executive, from having to answer questions at work about her fiance. They moved into an apartment in the Village, bought a place in the Hamptons, and kept dancing, even after the progression of Spyer’s illness, diagnosed in 1977, left her confined to a motorized wheelchair. They were among the first to register as domestic partners in New York City in 1993 and celebrated their 40th anniversary by getting married in Toronto—a marriage that was recognized by New York State because it was legal under Canadian law. Windsor was 77; Spyer was 75. The wedding was announced in the New York Times.But like many aging couples, the pair took a financial hit during the 2008 economic crisis, and when Kaplan went to meet Windsor, not long after Spyer’s death, she found Windsor—who could remember her family losing its home during the Depression—terrified about how to pay her mounting estate bills. “It was pretty obvious right away that this was the case,” Kaplan told me recently over pastrami sandwiches at DGS Delicatessen in Washington, D.C. “The number was so big, and the relationship she had with Thea—that was a marriage. To have and to hold.”Kaplan, who lives near Windsor in the West Village, was in Washington to rehearse her arguments in moot court sessions before legal scholars including Stanford’s Pamela Karlan, who co-directs the school’s Supreme Court litigation clinic. She was in a court-appropriate suit with a gray top and pink pearls, but her short blond hair looked as though she’d been pushing her fingers through it as she worked.At 46, Kaplan is the product of a different generation than Windsor. She and her wife, Rachel Lavine—a Democratic party operative whom Kaplan refers to in conversation as “my spouse”—married in 2005, also in Toronto, and had a son the following year. They are close to New York City mayoral candidate Christine Quinn and are fixtures on the Hamptons party circuit and on various nonprofit boards. The pair holds multiple synagogue memberships, though Kaplan’s primary attachment is to Jan Uhrbach, rabbi of the Conservative Synagogue of the Hamptons, who performed Kaplan and Lavine’s Jewish wedding ceremony. “I go every Saturday,” Kaplan told me. “It’s the closest I can get to meditation.”Kaplan grew up in Cleveland, Ohio, where her father and grandfather had a roofing business. Her mother, an ardent feminist, taught women’s history at a local community college—her specialty was Emma Goldman—and subscribed to New York magazine. At her bat mitzvah, Kaplan’s parsha was Shoftim, which includes the line “justice, justice shall you pursue,” and when she arrived at Columbia for law school, she signed up for a class in Talmudic law with Rabbi Saul Berman, one of Modern Orthodoxy’s leading thinkers. It was part of a Jewish progression that had brought her—dragging her family along—from their Reform congregation to a Conservative synagogue. “I was more religious than everyone else,” Kaplan told me. As a girl, she also insisted that her parents extend the annual family Seder to focus on the lessons of the Haggadah, rather than jumping immediately to the festive meal. “I never felt the need to assimilate,” Kaplan told me. “I said, ‘Wait, you attach all this importance to this ritual, so let’s make a big deal of it.’ ”She earned her undergraduate degree at Harvard, where she majored in Russian. She was in Moscow for her semester abroad in 1987, when the refusenik Yuli Edelstein, now an Israeli minister, was released from the gulag. “I had a sense of invincibility,” Kaplan, who says she was followed by secret police during her time in the Soviet Union, admits now. But she was quick to compare the Soviet Jewry movement just before the fall of the Berlin Wall to where she believes the marriage-equality movement is today. “Hopefully, knock on wood, it will be the same,” she said, tapping the table with her knuckles. “A lot of successes, quickly.”Just before we met for lunch, Sen. Rob Portman, the Ohio Republican, announced his newfound support for same-sex marriage, the latest in a string of turnarounds from prominent conservatives. But when Kaplan, who is a partner at Paul, Weiss—which she joined in part because it was known for being the first white-shoe New York firm to have Jews and non-Jews practicing together—initially took Windsor on as a pro bono client, it wasn’t clear that a cultural tipping point had been reached. California voters had just passed a referendum overturning a court ruling allowing same-sex marriages in the state, and at least one gay-rights organization had declined to take Windsor’s cause. (The challenge to the California measure, Proposition 8, will be heard before the Supreme Court on Tuesday, the day before Windsor’s case.)“She found Edie as a client, and she basically said, ‘I’m doing this case,’ ” said Jeffrey Trachtman, who litigated a companion same-sex marriage case before the New York Court of Appeals alongside Kaplan in 2006 and who authored a brief on behalf of more than a dozen religious movements and organizations, including Jewish ones, filed in Windsor’s case. “But this is the right case at the right time.”Kaplan never imagined the issue would reach the nation’s top court so soon and with such momentum for change behind it. “I would have said it was impossible,” Kaplan told me. “It’s a momentous occasion. There would be something wrong with me if I didn’t feel that way.” She was on her way to catch the Acela back to New York for Shabbat and had specially asked a friend to make her a roast chicken as a restorative. And because the arguments are scheduled to begin just hours after the second Seder, Kaplan plans to hold a meal in Washington for her family and members of her legal team—just another Jewish scheduling quirk in the case, which was scheduled for federal appeal last fall the day after Yom Kippur. But Kaplan said she would forgo a chicken and stick with her family tradition. “It will be brisket,” she said.***CORRECTION, March 24: An earlier version of this story reported that Jeffrey Trachtman argued a 2004 same-sex marriage case before New York’s Court of Appeals. Trachtman worked on the litigation, but the case was argued in court by Susan Sommer of Lambda Legal.Allison Hoffman is a senior editor at Tablet Magazine. Her Twitter feed is @allisont_dc.