It's hard to say. Stalin was the most oppressive, but his industrialization helped defeat Fascism. Hitler was brutal as well, but his plans single-handedly brought Germany from extremely poor to extremely prosperous during the Great Depression. Mussolini is not even close. I wouldn't put Mao up there either.
Mussolini would look like a fluffy rabbit compared to all other dictators. He believed in racial equality, until 1943 when he was forced to pass racial laws by Hitler. No prizes to the person who guesses which race he persecuted.
I believe Kim Jong Ill is one. All he has ever done for his country is to starve it, oppress it, increased military spending, isolate it, closed down trade, while he sits in his palace and eats rich food with wine.
At least other dicators have something to show. Hitler revived Germany, Stalin made the USSR a world power, Mussolini gave Italy more international recognition, Mao fought off the Japanese (before becoming a dictator).
But what has our dear friend Kim done? Stockpile on nuclear material, increased the NK drug trade, etc. He virtuall runs a criminal empire.
