5. Darth Thanaton
4. Marka Ragnos
Ruled the sith for a century, which when you think about it is an amazing feat in and of itself, set up the golden age of the sith.
3. Emperor Vitiate
Pretty much one-upped Ragnos by taking a broken down empire and rebuilding it to bloody the republic's nose.
2. Sidious
Cackling madman who somehow managed to make the Jedi and the rest of the galaxy look monumentally stupid. He was also pretty much the only good thing in the prequels, and that was after he shed his "nice senator" persona and went full on "UNLIMITED POWER" crazy.
1. Vader
The original, heavy breathing, force choking wonder. Not the kid whose emotional range is either whiny or bland, and not the Vader who shouts "NOOOOOOOOOO!" either.