Wyndham Mortimer (March 11, 1884 – August 25, 1966) was an American trade union organizer and functionary active in the United Auto Workers union (UAW). Mortimer is best remembered as a key union organizer in the 1937 Flint Sit-Down Strike. Mortimer was the First Vice President of the UAW from 1936 to 1939. A member of the Communist Party USA from about 1932, Mortimer was a critic of the efforts of the conservative American Federation of Labor to control the union and was a leader of a so-called "Unity Caucus" which led the UAW to join forces with the more aggressive Congress of Industrial Organizations (CIO).