Arthur Karl Greiser was a Nazi German politician, SS-Obergruppenführer, Gauleiter and Reichsstatthalter of the German-occupied territory of Wartheland. He was one of the persons primarily responsible for organizing the Holocaust in occupied Poland and numerous other crimes against humanity. He was arrested by the Americans in 1945, and was tried, convicted and executed by hanging in Poland in 1946 for his crimes, most notably genocide.

Obergruppenführer was a paramilitary rank in Nazi Germany that was first created in 1932 as a rank of the Sturmabteilung (SA) and adopted by the Schutzstaffel (SS) one year later. Until April 1942, it was the highest commissioned SS rank after only Reichsführer-SS. Translated as "senior group leader", the rank of Obergruppenführer was senior to Gruppenführer. A similarly named rank of Untergruppenführer existed in the SA from 1929 to 1930 and as a title until 1933. In April 1942, the new rank of SS-Oberst-Gruppenführer was created which was above Obergruppenführer and below Reichsführer-SS.