The most outstanding ideological authority of the movement in Stuttgart, during the time of Rau's political involvement there, was however Clara Zetkin. She was a founding member of the Second International, about whom Friedrich Engels once had written, that he liked her very much, while emperor Wilhelm II is said to have referred to her as the "worst witch in Germany". She had been living in a Stuttgart suburb since 1891 and, since then, been gathering a circle of Württemberg Marxists around her, among them Rau's friend Hoernle, who had been editing with her the magazine "Die Gleichheit". Her house, built in 1903 in Sillenbuch (now a part of Stuttgart), had become a meeting place of leading national and local left-wing and communist activists. It was also visited by international communist leaders like Vladimir Lenin, who stayed there overnight in 1907. In 1920, when Zetkin was elected to the Reichstag in Berlin, Hoernle and Rau moved to Berlin as well.