Adolf Hitler possibly killed people during the First World War, and he received the Iron Cross, Second Class, and the Iron Cross, First Class, in 1914 and 1918 respectively. That said, neither award were given to him for situations where he personally killed, and he spent most of the war as a runner, not in a combat role. The 1914 award was for rescuing a wounded officer (Major Engelhardt) under heavy fire, and the 1918 award was for his role as a runner. The citation given in 1918 was as follows:

"As a runner, his coolness and dash in both trench and open warfare have been exemplary, and invariably he has shown himself ready to volunteer for tasks in the most difficult situation and at great danger to himself. Whenever communications have been totally disrupted at a critical moment in a battle, it has been thanks to Hitler’s unflagging and devoted efforts that important messages have continued to get through despite every difficulty. Hitler received the Iron Cross Second Class for gallant conduct during the fighting at Wytschaete on 1 Dec. 1914. [He] fully deserves to be awarded the Iron Cross First Class."

Outside the possibility he killed during the First World War, there is no evidence to suggest that Hitler personally killed anyone (without buying into conspiracy theories).

Sources: Adolf Hitler a War Hero

Corporal Hitler and the Great War 1914-1918: The List Regiment