>>96282003 (OP)
The best villain my group had was a wizard that became a wizard with the sole motivational reason being to start a harem of succubi.
He spent decades working on a summoning spell that had permanence for those it summoned so they couldn't be banished back to hell, the being summon had extreme loyalty and put the happiness, well being, desire, happiness, comfort, etc above anything else.
Problem was that it didn't specify succubus because the wizard was kind of dip shit in a lot of ways. So it just kept bringing over a bunch of demons that have absolute loyalty to him and genuinely love the guy. So unbanishable are taking over the world in order to make him the unquestionable leader of the material plane.
The wizard is scared shitless of the stuff he summoned and is just rolling with it. The major infernal powers? They think it's hilarious so they aren't stopping anything. To be fair, 100% of the shit coming through that portal will absolutely drain his nuts and pamper him, but he finds them too revolting to do anything with.