Edith (Edie) Windsor, on the right, holds hands with Thea Clara Spyer the day of their wedding, after 40 years together, on May 22, 2007. By then, Spyer was suffering from multiple sclerosis and could move only one finger. 
In this photo taken in the 1960s, Thea Spyer, left, poses with Edith Windsor at The Cloisters, in Washington Heights, New York City. 
Thea Spyer, left, and Edie Windsor were together for 42 years until Thea's death in 2009. 
Edie and Thea dress for Halloween sometime in the 1980s, years before they really got married in Toronto, Canada, in 2007. Thea was in a wheelchair because of her MS. 
Thea and Edie age gracefully together. 
Edie, seen outside the Supreme Court building, was required to pay $363,000 more in estate taxes than she would have had to pay if the federal government recognized her 2007 marriage to Thea. 
Edie acknowledges her supporters as she leaves the Supreme Court on March 27 after arguments in her case challenging the constitutionality of the Defense of Marriage Act. - Edith Windsor won the Supreme Court case that overturned DOMA
- Windsor never thought she would be grand marshal of Pride Parade at 84
- She sued over a tax bill and it led to equality for same-sex married couples
- She was anguished that her government considered her marriage illegitimate
Editor's note: Edith Windsor was the plaintiff in the Supreme Court case challenging the Defense of Marriage Act.
(CNN) -- On Sunday, I will have the honor of serving as grand marshal in the New York City Pride Parade. I have marched in the parade for the last several years carrying a huge rainbow flag. Last year, I was so elated that I danced my way down the street for the entire route.
Before that, my late wife Thea and I, she in her wheelchair, would watch the parade together every year. If someone had told me 50 years ago that I would be the marshal of the New York City Gay Pride Parade in 2013 at the age of 84, I never would have believed it.
Over the past couple of years, many people have asked me, "Why did you decide to sue the United States over a tax bill?" Because the answer is complex, let me give you some of the background.
I lived with and loved my late spouse, Thea Spyer, for more than four decades in love and joy, and in sickness and health, until death did us part. When Thea died in 2009 from a heart condition two years after we were finally married, I was heartbroken.
On a deeply personal level, I felt distressed and anguished that in the eyes of my own government, the woman I had loved and cared for and shared my life with was not my legal spouse, but was considered to be a stranger with no relationship to me.
On a practical level, because of the so-called Defense of Marriage Act, or DOMA, I was taxed $363,000 in federal estate tax that I would not have had to pay if I had been married to a man named Theo instead of a woman named Thea. Even if I had just met Theo, married him and never even lived with him before he died, the tax would have been zero. So, overwhelmed with a sense of injustice and unfairness, I decided to file a lawsuit to get my money back.
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High court rules on same-sex marriage I lucked out when Robbie Kaplan, a litigation partner at the law firm of Paul Weiss, walked into my life. At a time when the gay organizations that I approached responded with, "It's the wrong time for the movement," Robbie Kaplan said -- as did the Rev. Martin Luther King Jr. before her -- "There is no wrong time" to seek justice. She answered my plea, and took me on.
Robbie argued my case in the Supreme Court on March 27 this year. When she argued against DOMA, she was cool and calm and informed and reasoned -- all of which was sustained by her deeply felt passion for equality in all of our lives. And we WON -- all the way.
I have been so honored and humbled to represent not only the thousands of Americans whose lives have been adversely impacted by DOMA, but those whose hopes and dreams have been constricted by that same discriminatory law.
Because of the historic Supreme Court ruling in my case, the federal government can no longer discriminate against the marriages of gay and lesbian Americans. Children born today will grow up in a world without DOMA. And those same children who happen to be gay will be free to love and get married -- as Thea and I did -- but with the same federal benefits, protections and dignity as everyone else.
To all the gay people and their supporters who have cheered me on, thank you. I'm sure that Thea is thanking you, too.
Not only does a much larger portion of the "straight" world see us differently -- as just people who live and love and play with their kids -- but also our own community has come out and seen each other, and loved each other, in a way that makes me courageous and proud and joyous every day.
If I had to survive Thea, what a glorious way to do it.
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The opinions expressed in this commentary are solely those of Edith Windsor.
