Sandra Day O'Connor (pictured) became the first female justice of the Supreme Court of the United States.

Sandra Day O'Connor was an American attorney, politician, and jurist who served as an associate justice of the Supreme Court of the United States from 1981 to 2006. Nominated by President Ronald Reagan, O'Connor was the first woman to serve as a U.S. Supreme Court justice. A moderate conservative, she was considered a swing vote. Before O'Connor's tenure on the Court, she was an Arizona state judge and earlier an elected legislator in Arizona, serving as the first female majority leader of a state senate as the Republican leader in the Arizona Senate. Upon her nomination to the Court, O'Connor was confirmed unanimously by the United States Senate.

An associate justice of the Supreme Court of the United States is a justice of the Supreme Court of the United States, other than the chief justice of the United States. The number of associate justices is eight, as set by the Judiciary Act of 1869.