Mogens Ludolf Fog (9 June 1906 - 16 July 1990) was a Danish physician, politician (Danish Communist Party) and resistance fighter. In the 1930s, he headed the Socialistiske Læger (Social Physicians) who opposed Fascism. After the war, he continued his political career, first as a Communist but in 1958 he left the Communist Party of Denmark and founded the Socialist People's Party together with Aksel Larsen.