Karl Rudolf Werner Best was a German jurist, police chief, SS-Obergruppenführer, Nazi Party leader, and theoretician from Darmstadt. He was the first chief of Department 1 of the Gestapo, Nazi Germany's secret police, and initiated a registry of all Jews in Germany. As a deputy of SS-Obergruppenführer Reinhard Heydrich, he organized the World War II SS-Einsatzgruppen, paramilitary death squads that carried out mass-murder in Nazi-occupied territories.

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.