At age 27, Heinrich Himmler, then a squad leader in the small personal security branch of the Nazi party, told the party's leader, Adolf Hitler, of his vision of transforming the party's security squads (Schutzstaffel, abbreviated SS, meaning Protection Squads) into a "racially pure" elite force, personally loyal to Hitler. Hitler approved, promoted Himmler to deputy nationwide leader of the SS, and a year later, on January 6, 1929, promoted Himmler to "Reichsfuhrer-SS" (nationwide leader-SS), which remained his title and rank for 16 years, until the end of Nazi Germany.
As head of the SS, Heinrich Himmler led one of the most outstanding power-hungry careers in history. SS membership increased from 280 to over a million, and the power and authority granted to him by Hitler continuously expanded, transforming the SS to a-state-within-a-state, making Heinrich Himmler the 2nd most powerful person in the Nazi regime. His powers eventually included:
The SS were initially just a unit of the SA that was responsible for protecting Hitler and other key Nazis, and maintaining security and order in the party's meetings. What Himmler offered to Hitler was to develop the tiny SS into a very different type of force. Under Himmler, the SS was strict about its recruitment requirements. In addition to fully documented "racial purity" (i.e. ethnic German origin), SS members were required to be intelligent, decent, reliable, self-disciplined, obedient, and totally loyal, ideologically and personally, to Hitler.
Instead of the hot-headed street gangs of the SA, the SS would murder anyone without hesitation, but only if ordered to. They would torture or murder a person, or mass-murder thousands, but would not loot, cheat, or brawl. They would murder even fellow Nazis, and even fellow SS men, if ordered to. They would act with calculated cold-blooded self-disciplined violence, in total personal obedience to Adolf Hitler (via Himmler's orders). When the Waffen-SS was formed, its recruitment requirements also included physical size and fitness, bravery and endurance, in order to form elite military units. And last, many high-ranking SS officials were highly-educated people with various doctoral degrees.
The SS men knew that they were the party's elite, later also the German people's elite, and Himmler did a lot to further enhance their esprit de corps, with their own unique uniforms, ranks, ceremonies, privileges, etc.
From Hitler's point of view, it paid off once he came to power in Germany. Whenever he needed to imprison or murder people, anyone from veteran Nazis to entire population groups, the SS did it efficiently, systematically, and at ever increasing scale. It vastly expanded during World War 2, as Nazi Germany invaded and occupied most of Europe, enslaved, deported, imprisoned, and mass-murdered, entire ethnic populations, especially but not only the Jews, in the most systematic cold-blooded genocide in history.