(13 August 1871 – 15 January 1919) was a German socialist and a co-founder with Rosa Luxemburg of the Spartacist League and the Communist Party of Germany. He is best known for his opposition to World War I in the Reichstag and his role in the Spartacist uprising of 1919. The uprising was crushed by the social democrat government and the Freikorps (paramilitary units formed of World War I veterans). Liebknecht and Luxemburg were killed.