William "Bill" Joseph Brennan Jr. (April 25, 1906 – July 24, 1997) was an American lawyer and jurist who served as an Associate Justice of the Supreme Court of the United States from 1956 to 1990. He was the seventh, longest serving justice in Supreme Court history, and known for being a leader of the U.S. Supreme Court's liberal wing. Due to his ability to shape a variety of wide opinions and "bargain" for votes in many cases, he was considered to be among the Court's most influential members. Justice Antonin Scalia called Brennan "probably the most influential Justice of the [20th] century."