Felix Frankfurter (November 15, 1882 – February 22, 1965) was an Associate Justice of the United States Supreme Court.

Frankfurter was born on November 15, 1882 in Vienna, Austria, third of six children of Leopold and Emma (Winter) Frankfurter. His forebears had been rabbis for generations. In 1894, when he was twelve, his family emigrated to the United States, where he learned English growing up on New York City's Lower East Side. Frankfurter attended P.S. 25 where he excelled at his studies, and enjoyed chess and crap shooting on the street. He spent many hours reading at The Cooper Union as well as attending political lectures, usually on subjects such as trade unionism, socialism and communism. After graduation from City College of New York in 1902, he worked for the Tenement House Department of New York City in order to raise money for law school. He applied successfully to Harvard Law School, where he excelled academically and socially. He made lifelong friends of Walter Lippmann and Horace Kallen, became an editor of the Harvard Law Review, and graduated with one of the best academic records since Louis Brandeis.

Due to the anti-semitism of the time, Frankfurter initially found it difficult to find employment after graduation. He joined the New York law firm of Hornblower, Bryne, Miller and Porter in 1906, and then in the same year became the assistant of Henry Stimson, the US attorney for the Southern District of New York. During this period, Frankfurter read Herbert Croly's book The Promise of American Life, and became a supporter of New Nationalism and Theodore Roosevelt. In 1911, President William Howard Taft appointed Stimson as his Secretary of War and Stimson appointed Frankfurter as law officer of the Bureau of Insular Affairs, though Frankfurter in fact worked as Stimson's assistant and confidant. His government position restricted his ability to publicly voice his progressive views, though he expressed his opinions clearly in private to friends such as Judge Learned Hand. In 1912 Frankfurter supported the Bull Moose campaign to return Roosevelt to the presidency and was bitterly disappointed when Woodrow Wilson was elected. He became increasingly disillusioned with the established parties, and described himself as "politically homeless".