Sandra Day O'Connor

First woman to serve on the Supreme Court, appointed by President Reagan in 1981 and serving until 2006. O'Connor was the decisive fifth vote in dozens of landmark decisions on abortion rights, affirmative action, and campaign finance, making her the most consequential swing justice of the twentieth century. She wrote the plurality opinion in Planned Parenthood v. Casey (1992), which preserved Roe v. Wade while allowing new restrictions.