Robert Nelson Cornelius Nix Sr. (August 9, 1898 – June 22, 1987) was an American politician who served in the United States House of Representatives from 1958 until 1979. He was the first African American to represent Pennsylvania in the House of Representatives. The Robert N. C. Nix Federal Building in Philadelphia, Pennsylvania is named in his honor.
Born in Orangeburg, South Carolina, he attended Townsend Harris High School in New York City and graduated from Lincoln University (Pennsylvania) in 1921. He received his law degree from the University of Pennsylvania and began practicing in Philadelphia. After entering private practice, Nix became active in the Democratic Party as a committeeman from the fourth ward in 1932. He became a special assistant deputy attorney general of Pennsylvania in 1934 and delegate to the 1956 Democratic National Convention.
In 1958, he defeated two opponents in a special election to fill a congressional vacancy left by Earl Chudoff in the House of Representatives. An elected official who rarely wanted or attracted widespread publicity, he supported mostly liberal legislation. He was reelected 10 times. He worked for the passage of the landmark legislation promoting the American Civil Rights Movement and privately sought to prevent the House from denying Rep. Adam Clayton Powell his seat in 1967. In 1962, he became the first member of congress to knowingly meet with gay activists, when he invited Frank Kameny to his office. In 1975, he introduced an amendment to the Foreign Military Sales Act requiring the Defense Department to provide the U.S. Congress with information on identities of agents who negotiate arms sales for American firms.