It would be very interesting to say Hitler, thereby proving Godwin's Law, but I feel that the legacy of World War II is a mixed bag, as horrible as the Holocaust was. Instead, I am going to go with someone involved with WWII who is often overlooked as someone to "erase" in these kinds of questions.
Josef Stalin
When Lenin died, it was quite a close call between Stalin and Trotsky over who would be his successor. The Soviet Union was not a totalitarian regime at the time. Stalin took it in that direction, and it is not inevitable that Trotsky would have done the same. Yes, under Stalin's regime the Soviet Union experienced a great amount of economic growth, but at a tremendous cost that ended up being larger than the amount that died under Nazi rule in Germany. While Stalin's gulags were more for political than ethnic prisoners, it was pretty much for anyone whom he had any sort of slight problem with. Further, it was the Stalinist Soviet Union that really started the whole "Red Scare" in the U.S. that led to the Cold War and the branding of Communism as inevitably leading to such totalitarian regimes. The Cold War itself was really a shameful period in the foreign policies of both the U.S. and Russia/U.S.S.R., that I am sure both would take back in a heartbeat. Under Stalin, the Soviets did win WWII, but then placed the entirety of Eastern Europe under their harsh sphere of influence, dragging the region's growth to a stunted pace as compared to that of Western Europe and North America. Really, anything Stalin touched turned to crud. And I feel the Soviets and the Allies could have still won the war under Trotsky, even if they avoided going totalitarian. History would have looked a lot different. Whether that would be for the better or worse is unknown, but it would be hard to be worse than what Stalin did to the U.S.S.R. So that's who I would "erase" from history.
