Edith Windsor, the gay rights activist who sued the US federal government to recognise her same-sex marriage, has died aged 88.
She became an icon within the LGBT community when she won a landmark 2013 US Supreme Court case against the government to recognise her marriage.
The case was widely considered to lay the foundation for the decision to legalise same-sex marriage across the United States in 2015.
Mrs Windsor died in New York aged 88 on Tuesday, her lawyer Roberta Kaplan said.
The cause of death wasn't given, but Mrs Windsor had struggled with heart issues for years.
Current spouse Judith Kasen-Windsor, whom Mrs Windor married last year, said: “The world lost a tiny but tough-as-nails fighter for freedom, justice and equality."
Mrs Windsor became a gay rights pioneer after her first spouse, Thea Spyer, died in 2009.
The women had married legally in Canada in 2007 after spending more than 40 years together.
Mrs Windsor sued the federal government after her wife's death, saying its definition of marriage as a relationship between a man and a woman prevented her from getting a marital deduction on her estate.
That meant she faced a huge tax bill that heterosexual couples would not have.
The US Supreme Court ruled in June 2013 that the provision in the law was unconstitutional, and that legally married same-sex couples are entitled to the same federal benefits that heterosexual couples receive.
The landmark opinion gave the nation's legally married gay couples equal federal footing with all other married Americans and marked a key moment of encouragement for gay marriage supporters confronting the nationwide patchwork of laws that, at the time, outlawed such unions in roughly three dozen states.
Ultimately, the opinion in Mrs Windsor's case became the basis for the wave of federal court rulings that struck down state marriage bans and led to a 2015 Supreme Court ruling giving same-sex couples the right to marry.
Anthony Romero, executive director of the American Civil Liberties Union, called Mrs Windsor "one of this country's great civil rights pioneers."
"One simply cannot write the history of the gay rights movement without reserving immense credit and gratitude for Edie Windsor," Romero said.
Mrs Windsor said she was "honoured," `'humbled" and "overjoyed" when the decision came down. According to The New Yorker magazine, she called a friend and said, "Please get married right away!"
She was a finalist for Time magazine's Person of the Year in 2013 - although Pope Francis ultimately got the honour - and was invited the next year to a state dinner at the White House, honouring then-French President Francois Hollande.