The main security force of Hitler was called the SS (Schutzstaffel). It was founded in 1920 and was headed by Heinrich Himmler for most of its lifetime. Under Himmler, it grew into one of the most powerful forces in Europe and was responsible for most of the crimes committed by Germany during the Second World War.
Its main objective was to establish the racist utopia as envisaged by Hitler. As part of this objective, it established a chain of extermination camps across occupied Europe. Millions of Jews and other people the Nazis considered undesirable were deported to these camps to be enslaved and murdered in gas chambers. The SS was also responsible for maintaining internal security in the German Reich. As part of this function, it persecuted and murdered many opponents of the Nazi regime.
For the leading role it played in committing crimes against humanity, the SS was declared a criminal organization by the International Military Tribunal in Nuremberg, and banned in Germany after 1945. Leaders of the SS either committed suicide or were executed after Germany's defeat.