Karl Paul August Friedrich Liebknecht (; 13 August 1871 – 15 January 1919) was a German socialist politician and theorist, originally of the Social Democratic Party of Germany (SPD) and later a co-founder with Rosa Luxemburg of the Spartacist League and the Communist Party of Germany, which split from the SPD after World War I. He is best known for his opposition to the war in the Reichstag and his role in the Spartacist uprising of January 1919. The uprising was crushed by the SPD government and the Freikorps (paramilitary units formed of World War I veterans), which summarily executed Liebknecht and Luxemburg.