Frankfurter was born in Vienna, Austria, and immigrated to New York City at the age of 12. After graduating from Harvard Law School, Frankfurter worked for Secretary of War Henry L. Stimson. During World War I, Frankfurter served as Judge Advocate General. After the war, he helped found the American Civil Liberties Union and returned to his position as professor at Harvard Law School. He became a friend and adviser of President Franklin D. Roosevelt, who appointed him to fill the Supreme Court vacancy caused by the death of Benjamin Cardozo.