Justice William Brennan was an influential Associate Justice of the United States Supreme Court, serving from 1956 to 1990. Appointed by President Dwight D. Eisenhower, he became known for his strong advocacy of civil rights and liberties, significantly shaping constitutional law during his tenure. Brennan was a key figure in landmark cases involving freedom of speech, abortion rights, and racial equality. His opinions often emphasized the importance of individual rights and the need for the Constitution to adapt to changing societal values, making him a pivotal voice in the Court's history.