Sturmführer was a paramilitary rank of the Nazi Party which began as a title used by the Sturmabteilung in 1925 and became an actual SA rank in 1928. Translated as “Storm Leader,” the origins of the rank dated to the First World War when the title of Sturmführer was used by leaders of German Shock Troops and Special Action Companies.
By 1930, Sturmführer had become the first officer paramilitary rank of several Nazi Party organizations. The title was also used as an SS rank until 1934 when, after the Night of the Long Knives, the SS renamed the rank as Untersturmführer. Other variations of Sturmführer included Obersturmführer and Hauptsturmführer, considered higher ranking paramilitary officers to a regular Sturmführer.
Source: Wikipedia; Picture courtesy of: U.S. National Archives.