Key words: The “Subterranean Emperor”
Underworld mob boss, that acts like an emperor. Operating in the lowest part of a city, in its “underworld”. Commanding a huge “army” of criminal underlings.
The Set: Emperors main place of operation, a high end office with a massive window show casing the run down under city as a back drop.
The initial problem I can see with this idea is that it may be visually boring, the city scap would play a big role, along with the lighting of the room.
Evil Emperor, hell-bent on returning from the afterlife to seek revenge on the human race for imprisoning him in the underworld.
The roman version of the afterlife comes to mind.
The Set: Massive throne room with the Throne being the center piece. The Hero Prop being his massive sword, or perhaps a magic book which he hopes to use to escape from the afterlife.
The human race has moved underground due to the surface being uninhabitable. The Emperor is a title or name used by a Robin Hood type character, who steals food and water and gives it to the poor.
The Set: Metal underground themed city, our hero resides in a secluded room near the deepest part of the underground world, next to the generators and air producing machines.