Rosa Luxemburg (1871–1919)
Rosa Luxemburg championed the idea of the mass strike. In 1914 she became a tireless opponent of WWI. Because of their approval of the war she renounced the German Social Democracy, helped to create the Spartacus League, and later the German Communist Party. Luxemburg was critical of the Soviet government. In 1919 she got executed by the German government in the aftermath of a failed uprising.
Rosa Luxemburg archive in English in the Marxist’s Internet Archives: