Adolf Hitler was a major World War II figure and the dictator of Nazi Germany from the early 1930s until he committed suicide in 1945. Although he killed a lot of people, primarily Jews, he didn't kill as many people as Soviet Russian dictator Josef Stalin.
After his fall from power, he became a widely-targeted subject of ridicule. He is often depicted, in animutation and other mediums, prancing around like a fanatical little moron. During the wartime years, he was "honoured" with the hit Spike Jones song, "Der Fuhrer's Face", and its companion animated short, which starred Donald Duck.
He is often used in animutations, to the point where he is considered a recurring character. His biggest role is We Drink Ritalin, where he and Alex Chiu are the stars of said animutation. He also killed Mattress Giant's mother in Exotic Japan, where Mattress Giant would soon be killed by Hitler as well. An image of him used in animutations sometimes is an animated gif showing him dancing.