Robert Emmet Hannegan (June 30, 1903 – October 6, 1949) was an American politician who served as Commissioner of Internal Revenue from October 1943 to January 1944. He also served as chairman of the Democratic National Committee from 1944 to 1947 and United States Postmaster General from 1945 to 1947. At the conclusion of his political career in 1947, Hannegan and his business partner Fred Saigh purchased the St. Louis Cardinals, a Major League Baseball team. But Hannegan, by then ill with heart disease, sold his share of the team ownership to Saigh a few months before his death.