In 1925, Heinrich Himmler joined the unit, which had by then been reformed and given its final name. Under his direction (1929–1945) it grew from a small paramilitary formation during the Weimar Republic to one of the most powerful organizations in Nazi Germany. From 1929 until the regime's collapse in 1945, the SS was the foremost agency of security, surveillance, and terror within Germany and German-occupied Europe.