A RANCHER’S DAUGHTER, Sandra Day O’Connor learned as a child to excel in what was then considered a man’s world. Her skill at shooting and riding was outshone only by an intellect first honed by her early education in El Paso and ultimately validated by her appointment as the first woman associate justice on the U.S. Supreme Court. Today O’Connor is the court’s key swing vote; her opinions have long defied pigeonholing, in part because—as a wife, lawyer, mother, and judge—she both embraced and bucked tradition. Her vast knowledge of the law has led to welcome revisions of outdated ideas—for example, the Supreme Court’s 1872 assertion that “it belongs to men to make, apply, and execute the law.”

She was born Sandra Day on March 26, 1930, in El Paso, and spent her first five years and her summers on her parents’ remote Arizona ranch. In 1935 she was sent to El Paso to live with her grandmother and attend school there.

At age sixteen she entered Stanford, earning both a bachelor of arts and a law degree. She married fellow law student John Jay O’Connor in 1952.

After graduating, she was turned down by every law firm she applied to except one, which offered her a job as a legal secretary. She later worked as a civilian lawyer for the Army and accompanied her husband, who was in the service, overseas.

In 1957 they moved to Phoenix, where she briefly practiced law before postponing her career to raise their three sons.

Her volunteer work for local Republicans paid off in 1969, when she was appointed to fill a vacant state senate seat. She supported the Equal Rights Amendment but distanced herself from feminists, assuring one audience, “I come to you tonight wearing my bra and my wedding band.”

In 1974 she was elected a county judge and became known for tough but fair rulings. Five years later Governor Bruce Babbitt appointed her to Arizona’s court of appeals.

On July 7, 1981, Ronald Reagan nominated her to fill the U.S. Supreme Court vacancy left by retiring associate justice Potter Stewart. The U.S. Senate confirmed her in a unanimous vote.

In 1988, at age 58, she found out she had breast cancer. She scheduled her chemotherapy on Fridays so she wouldn’t miss work. She is famed for exercising daily in the court’s gym before arriving at her chambers, which are decorated with baskets, rugs, and other crafts of her native Southwest.