Karl Liebknecht 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. Liebknecht and Luxemburg were killed. After their deaths, Karl Liebknecht and Rosa Luxemburg became martyrs for Socialists. According to the Federal Office for the Protection of the Constitution, commemoration of Liebknecht and Luxemburg continues to play an important role among the German far left.

https://en.wikipedia.org/wiki/Karl_Liebknecht