Baator

Baator (BAY-uh-tor), also known as the Nine Hells of Baator or the Nine Hells, is a plane of tyranny and oppression under the iron grip of Asmodeus.

In the Great Wheel model of the multiverse, Baator is the Lawful Evil Outer Plane. In the World Axis, it is considered an evil astral dominion. In the World Tree, it's considered a fiendish plane.

Regardless of which cosmological model you prefer, no one disputes that Baator is a world of cruelty and ruthlessness under the absolute rule of a single mind: that of Asmodeus. No word is whispered here that is unheard by Asmodeus. No secret is hidden from his ever-watching eye. It is a plane of conformity, totalitarianism, and bureaucracy.