I'm looking for a novel where the MC is transported to another world, but his role in the previous world was that of a typical villain and is now still important on how the story progresses (how the MC acts) in the new world, like Diablo role-playing as a Demon King or Ainz Ooal Gown being one of the Forty-One Supreme Beings. I'm mostly searching for someone like Ainz (cold, seen as evil by the world and taken seriously by his subordinates) rather than some like Diablo (kind, none of the people who actually know him taking his claims seriously), but both are examples of what I'm looking for overall.
Does it have to be a Isekai? If not I would recommend Maou Gakuen no Futekigousha. MC (Demon King) lets himself be killed to finally bring a stop to the constant war, before his death he prepared a reincarnation spell so that he could see the peace one day. Now 2000 years later he is reborn. For the MC he can be very nice to those he cares about but for his enemies death would be your least problem. On his first outing he met with some arrogant brat so to discipline him he killed and revived him several times, in quite the brutal ways.
That's kind of the opposite. He sees himself as a villain but everyone else sees him as a hero. The ones that immediately come to mind for me are The Death Mage Who Doesn't Want a Fourth Time To Be a Power in the Shadows! Kumo Desu ga, Nani ka? (reincarnated into a spider that makes people wet themselves, but lacks subordinates)
"Dungeon Defence". Basicallу Overlord but the MC is much more interesting to watch. The MC is batshit crazy,cуnical,shrewd and an eloquent bastard. All the other characters are just as crazу and interesting. .
Haven't read before, thanks! Already reading. It is similar to Isekai Maou, but the novel takes itself a lot less seriously. Liam is very childish. Differently from Diablo, who at the least understands what would be actually evil to do and isn't really a villain at heart, Liam aims to be an evil lord, but fails. He is pretty naive on the entire concept of evil and never really takes direct action on his own to commit actual evil, rather he delegates all his political/economical power to his subordinates, who act on his very vague orders open to interpretation however they see fit and make him a hero. I'm looking for something more dark or serious. No, it doesn't have to be an Isekai. It's sufficient for the MC to be in unfamiliar surroundings. The novel sounds very interesting! Dropped Death Mage because of the plot seemingly having no actual overall direction and the randomness of it all. To Be a Power in the Shadows! - He aims to be a "good Power in the Shadows" and the novel doesn't take itself seriously, so his identity is unimportant overall. Kumo Desu Ga, Nani Ka - It's been a long time since I last read this and I vaguely recall the plot being all over the place, but I'll take another stab at it. Already read, unfortunately.
Death Mage and Kumo are both sort of the same in that the real plot involves the gods, so it's veiled in mystery early on while the MC is still just trying to survive. The reason those two have such great followings is because the plot gets more interesting with time, unlike most web novels which start great and then fizzle.