by Karl Berg, there is no widely recognized thriller series with that exact "Zirkel" (Circle) branding reaching a 17th installment.
Despite its notoriety, Der Sadisten Zirkel 17 was eventually disbanded in the early 1930s, likely due to increased scrutiny from law enforcement and the public. The group's legacy has endured, however, and it remains a fascinating and disturbing footnote in the history of Berlin's avant-garde and countercultural movements. Der Sadisten Zirkel 17