I like Cromwell. Especially since I just spent a fortune on Christmas presents ;)
I can think of many famous people who are considered evil, and have certainly caused a lot of pain to a lot of people (Hitler is an obvious favourite there), but it depends on whether we are talking about intentions or result. For example, the whole Bush family may have had good intentions of making the world a better place, and I have no reason to doubt their heart was in the right place, but Quantanamo is just as bad as any WWII concentration camp, and many of the people in it just as innocent. In fact, people were herded to Quantanamo based solely on their religious beliefs, which is exactly what happened in Dachau.
But if you want personalised, sadistic evil, then go no further than the Spanish Inquisition. Any of the people that were involved in that must have been so cruel, that Hannibal Lector pales by comparison. They constantly managed to devise new ways of torture to make pain even more acute and unbearable. How sick is that?