Retired Justice Sandra Day O'Connor, the first woman on the US Supreme Court, whose centrist views and shrewd negotiating skills allowed her to steer the nation's law for much of her quarter-century tenure, has died aged 93.
The court said in a statement on Friday that O'Connor died in Phoenix, Arizona of complications related to advanced dementia and a respiratory illness.
Chief Justice John Roberts recalled O'Connor as having "blazed an historic trail as our nation's first female justice".
"She met that challenge with undaunted determination, indisputable ability, and engaging candour," Roberts said.
"We at the Supreme Court mourn the loss of a beloved colleague, a fiercely independent defender of the rule of law, and an eloquent advocate for civics education."
O'Connor, who retired from the United States' highest court in 2006, had in her latter years been diagnosed with dementia and announced in October 2018 that she was withdrawing from public life.
When Republican former President George W Bush replaced the pragmatic westerner with the more ideologically rigid conservative Justice Samuel Alito, the already-conservative court moved further to the right.
O'Connor, who grew up on an Arizona ranch, navigated the male-dominated world of politics in her home state and then of law in the nation's capital. Her 1981 appointment by Republican President Ronald Reagan made her the Supreme Court's first woman justice nearly two centuries after the Supreme Court was established in 1789 but her place in history went beyond breaking men-only barriers.
Although she was conservative by nature, she became the court's ideological centre. With pragmatism and a knack for building consensus, she controlled decisions on the most contentious issues of her era, including helping preserve a woman's right to abortion and upholding affirmative action on college campuses.
O'Connor described her tenure as similar to walking on wet cement "because every opinion you offer, you've left a footprint".
O'Connor avoided sweeping pronouncements and voted for incremental change, becoming a pivotal vote on the court in the process. Her views became more liberal with time. After expressing some ambivalence about Roe v. Wade, the 1973 decision that made abortion legal nationwide, she created a critical alliance in 1992 to affirm Roe's central holding.
"Some of us as individuals find abortion offensive to our most basic principles or morality but that cannot control (the court's) decision," she wrote.
The Supreme Court, which has had a 6-3 conservative majority since 2020, overturned the landmark Roe ruling in 2022.
O'Connor's views on gay rights evolved, too. In 1986 she voted to uphold a Georgia law prohibiting sexual relations between homosexuals but voted in 2003 to strike down a similar law in Texas.
O'Connor was with the majority when the court ruled 5-4 on ideological lines to stop the Florida presidential vote recount, ensuring that Republican George W Bush candidate won the presidency over Democrat Al Gore in 2000.
She later expressed regret about the ruling, telling the Chicago Tribune in 2013 that the court did not need to get involved.
She raised awareness of breast cancer, which she survived in 1988 after a mastectomy, and the importance of research into Alzheimer's disease, which afflicted her husband. She retired in January 2006 to take care of him until his death in 2009.
After leaving the bench, O'Connor dedicated herself to improving civics education, starting a group called iCivics that provided free online resources for middle and high school students.
In 2009, Democratic former President Barack Obama presented her at the White House with the Presidential Medal of Freedom, the highest civilian honour a president can give.
Australian Associated Press