Adolf Hitler is the authoritative dictator of Germany and the leader of the Nazis in the TMNT comic book series, who is well-known for his actions in the Holocaust and World War II.
Hitler's brain was still functionional decades after World War II and powered a time machine. Obtaining a robot body, Hitler travels back to World War II to find his past self. The Hitler from the future was destroyed by the Turtles while the Past Hitler tries to get the brain only to be punched by Raphael.
Hitler points a gun at the Turtles just as they were about to leave. Leonardo convinces Hitler that he is in Hell and they are demons that have come for his brains. They told the dictator that they already have his soul. Hitler shoots himself in the head so the Turtles can't recover his brain.