I remember hearing that the actor who played Emperor Palpaltine found the character surprisingly difficult to play, because no matter how hard he tried he could not fine one humanizing trait or characteristic. All he found in The Emperor was pure selfishness, manipulation, and cold heartedness. Pretty evil to me.
Davros from Doctor Who is pretty evil. The guy ruthlessly massacred his own race, at one point feed unknowing people from many different worlds their dead loved ones, created the Daleks and even attempted to destroy all of reality!