Adolf Hitler was the Chancellor (a kind of Prime Minister) in the 1930s in Germany. He was the person to lead Germany into the Second World War. He committed suicide at the end of the war when it was clear that Germany had lost the war.
Hitler was born in Austria and fought in the First World War. He come to power as leader of the National Socialist Party (known as the Nazi Party) during the 1930s when Germany was suffering after the war. There was a weak government and people listened to those who said that they could make Germany a powerful and proud country again.
So the elected him to government and, for a time, everything did seem to be going well. But many dark things were also happening, including many killings and persecutions of groups of people.
Gradually Hitler told that it was necessary to fight to get their natural homeland back, and so he took Germany to war.