Complete Monster: Randall Flagg is an Evil Sorcerer in the medieval country of Delain. Here, Flagg has Queen Sasha murdered, poisons King Roland, frames Prince Peter for the crime, and then plunges Delain into a new Dark Age by manipulating the remaining heir, Thomas.
Genius Bonus: Lucifer derives from the Latin lucem ferre, meaning "lightbringer". As in, Thomas the Lightbringer.
Lighter and Softer: By Stephen King standards, anyway. It's still pretty dark, but it's written for a slightly younger audience than King's normal work.