I'm trying to figure out if we're all talking about the same story here, because I've stumbled into a few different manhwa that kind of fit that phrase. If you mean the really popular one that was adapted from a novel, it's probably 'Dungeon Defense' (or sometimes 'Dungeon Attack'), the one where the main character gets reincarnated as the weakest dungeon lord from a video game. The protagonist is Dantalian, who starts as a weak demon but uses his incredible strategic mind and knowledge of the game's events to climb the demon ranks. He's cold, calculating, and ruthless, and he's surrounded by some wild characters like Laura, the fallen angel who ends up as his first and most loyal (and kinda yandere) subordinate. There's also a princess, Elizabeth, who gets dragged into his schemes, and his rival, the hero Karnon. The power plays and mind games between Dantalian and everyone else are the whole point. The cast is pretty big, but those are the pillars.
But honestly, I need to vent about the tone shift from the source material. The manhwa streamlines a lot and focuses more on the action, while the original webnovel is super dense with political maneuvering and internal monologues. The characters still come through, especially Dantalian's almost scary detachment, but some of his interactions with characters like the succubus Orcas feel different. If you're coming from the novel, the manhwa's version of characters can seem a bit simplified. I still think it's a fun ride, but I hope people know there's a deeper story in the text if they ever get curious. The art does a solid job of bringing the demon designs to life.