Heinrich Luitpold Himmler (German: [ˈhaɪnʁɪç ˈluːɪtpɔlt ˈhɪmlɐ] ; 7 October 1900 – 23 May 1945) was a German Nazi politician and military leader who was the 4th Reichsführer of the Schutzstaffel (Protection Squadron; SS), a leading member of the Nazi Party, and one of the most powerful people in Nazi Germany. He is primarily known for being one of the main architects of the Holocaust.

After serving in a reserve battalion during World War I without seeing combat, Himmler went on to join the Nazi Party in 1923. In 1925, he joined the SS, a small paramilitary arm of the Nazi Party that served as a bodyguard unit for Adolf Hitler. Subsequently, Himmler rose steadily through the SS's ranks to become Reichsführer-SS by 1929. Under Himmler's leadership, the SS grew from a 290-man battalion into one of the most powerful institutions within Nazi Germany. Over the course of his career, Himmler acquired a reputation for good organisational skills as well as for selecting highly competent subordinates, such as Reinhard Heydrich. From 1943 onwards, he was both Chief of the Kriminalpolizei (Criminal Police) and Minister of the Interior, which gave him oversight of all internal and external police and security forces (including the Gestapo). He also controlled the Waffen-SS, a branch of the SS that served in combat alongside the Wehrmacht (armed forces) in World War II.

As the principal enforcer of the Nazis' racial policies, Himmler was responsible for operating concentration and extermination camps as well as forming the Einsatzgruppen death squads in German-occupied Europe. In this capacity, he played a central role in the genocide of an estimated 5.5–6 million Jews and the deaths of millions of other victims during the Holocaust.