Adolf Hitler was the leader of Nazi Germany from 1934 to 1945, known for his totalitarian regime and the instigation of World War II through aggressive expansionist policies. His ideology was rooted in fascism, extreme nationalism, and anti-Semitism, which led to widespread atrocities, including the Holocaust. Hitler's rise to power and subsequent actions had profound effects on global history, marking a pivotal moment that altered the course of the 20th century.