Reichsführer-SS was both a title and a rank. The title of Reichsführer was first created in 1926 by the second commander of the SS, Joseph Berchtold. Julius Schreck, founder of the SS and Berchtold's predecessor, never referred to himself as Reichsführer. Yet, the title was retroactively applied to him in later years. In 1929, Heinrich Himmler became Reichsführer-SS and referred to himself by his title instead of his regular SS rank of Obergruppenführer. This set the precedent for the commander of the SS to be called Reichsführer-SS.
Under its original inception, the title and rank of Reichsführer-SS was the designation for the head of the Allgemeine-SS (General-SS). In this capacity, the SS Reich Leader was the direct commander of the SS Senior District Leaders (SS-Oberabschnitt Führer); by 1936, the Reichsführer-SS was head of the three main SS branches: the Allgemeine-SS, SS-Verfügungstruppe (SS-VT; Political Action Troops), and the SS-Totenkopfverbände (SS-TV; Concentration Camp Service).
During the Second World War, the Reichsführer-SS in effect held several additional roles and wielded enormous personal power. He was responsible for all internal security within Nazi Germany. He was overseer of the concentration camps, extermination camps (through the Concentration Camps Inspectorate and SS-TV), and the Einsatzgruppen mobile death squads (through the Reich Security Main Office; RSHA). Over time, his influence on both civil and foreign policy became marked, as the Reichsführer reported directly to Hitler and his actions were not tempered by checks and balances. This meant the office holder could implement broad policy, such as the Nazi plan for the Genocide or extermination of the Jews, or order criminal acts such as the Stalag Luft III murders, without impediment.
It is difficult to separate the office from the duties assigned to the individual. As of 20 April 1934, Himmler in his position of Reichsführer-SS already controlled the SD and the Gestapo. On 17 June 1936 Himmler was named chief of all German police, thereby placing all uniformed police (Orpo) and criminal police (Kripo) in Germany under his control. In the latter role, he was nominally subordinate to the Interior Minister, Wilhelm Frick. It is not clear how much of this power would technically reside in the office of the Reichsführer-SS were those duties to be split up. These questions became moot by the time Himmler became the Interior Minister in 1943.
It is difficult to define precisely the full detailed duties and responsibilities of the Reichsführer-SS beyond that of leader and senior member of the SS, since, in the words of historian Martin Windrow, "by the outbreak of the (Second World) war it would have been impossible to define exactly the role within the state" of the entire SS itself.