Karl Harrer was a journalist and one of the founding members of the "Deutsche Arbeiterpartei" ("German Workers' Party", DAP) in 1919, the party that soon would become the Nationalsozialistische Deutsche Arbeiterpartei (NSDAP).
Harrer was also a member of the right-wing Thule Society, who gave him the task of founding a "Politischer Arbeiterzirkel" ("political workers' union"), an order he carried out together with Anton Drexler in October 1918. On January 5 1919, this led to the founding of the DAP in which not only Harrer and Drexler but also Gottfried Feder and Dietrich Eckart were involved.
Harrer became the party's first chairman (adopting the title of "Reichsvorsitzender"); however, his plans to continue the DAP as a secret society similar to the Thule Society collided with Adolf Hitler's, who had also soon joined the party. Towards the end of 1919, their rivalry became more and more apparent; Harrer accused Hitler of megalomania, and ultimately resigned from all party offices and left the party after pressure from Hitler.