Just a thought...When we get to play Star Wars the Old Republic the emperor is over 1300yrs. old. So I think he needs an Honorable mention here because how the hell does someone use the Dark side that long without being worn out! Also from swtor Darth Malgus is the Dark Lord of the Sith who takes out the Jedi Temple (with help). The Emperor is His boss so whats up with Him? More expanded universe books are coming out for Star Wars the Old Republic so we all will get some new info.
1. Luke
2. Sidious
3. Yoda
4. Caedus (originally Mace, but I changed my mind)
5. Galen
6. Mace
7. Nihilus
8. Bane
9. Dooku
10. Anakin, Obi Wan and Vader
This isn't taking unknowns into account, since they're unknowns. It also isn't taking things such as orbalisks/amulets into account, nor is it taking Zenoma Sekot/Abeloth/other beings like that.
__________________ Introduce a little government. Upset the established gangs, and everything becomes order...
Democracy is the very definition of awesome.