Who was the first female Supreme Court Justice in the United States?

Sandra Day O'Connor was the first female Supreme Court Justice in the United States, appointed by President Ronald Reagan in 1981. Her appointment marked a significant milestone in U.S. history as it broke the gender barrier in the highest court of the land. O'Connor served on the Supreme Court until her retirement in 2006 and was known for her centrist views and pivotal role in many important decisions, often casting the deciding vote in closely contested cases.

The other justices mentioned were influential in their own rights, with Ruth Bader Ginsburg being a prominent voice for gender equality, Elena Kagan known for her work on the court following O'Connor’s tenure, and Sonia Sotomayor being the first Hispanic and Latina Justice. However, all of them came after O'Connor, who holds the distinction of being the first woman to serve on the Supreme Court.