" For the moment it was enough that his advisers and minions respected him–for reestablishing peace, for eliminating the group that had posed the greatest threat to continued stability–but eventually those same advisers would need to fear him. To understand the great power he wielded, as both Emperor and Dark Lord of the Sith. And to that end, Sidious needed Vader. For if someone as potent as Vader answered to the Emperor, then how powerful must the Emperor be! "

― James Luceno , The Rise of Darth Vader (Star Wars: The Dark Lord Trilogy, #3)