Adolf Hitler caused the murder of at least 5.5 million Jews during the Holocaust.
Adolf Hitler . As dictator of the German Reich , he initiated World War II in Europe with the invasion of Poland in September 1939 , and was central to the Holocaust . Under Hitler 's leadership and racially motivated ideology , the Nazi regime was responsible for the genocide of at least 5.5 million Jews and millions of other victims whom he and his followers deemed Untermenschen ( `` sub-humans '' ) and socially undesirable . Holocaust victims . According to the United States Holocaust Memorial Museum ( USHMM ) , the country 's official memorial to the Holocaust , `` The Holocaust was the murder of six million Jews and millions of others by the Nazis and their collaborators during World War II . '' The Holocaust ( from the Greek ὁλόκαυστος holókaustos : hólos , `` whole '' and kaustós , `` burnt '' ) , also referred to as the Shoah ( Hebrew : השואה , HaShoah , `` the catastrophe '' ) , was a genocide in which some six million European Jews were killed by Adolf Hitler 's Nazi Germany , and the World War II collaborators with the Nazis .