Among the souls that were sent to the Underworld from the Multidimensional Plane, there would always be some who stayed in Hell due to special circumstances. By chance, they would become "Undead of Hell". As time passed, more and more undead appeared, and now they were all over the Hell.
The other type was the nobles of Hell, the true natives and the managers of the Nine Hells:
They were demons!
The first and second levels of Hell were ruled by the imps.
From the third to the fifth level, there were devil lords and it was further divided into baron, earl, and duke.
After the sixth level would be the Grand Duke, who was comparable to a primordial soul wizard and was extremely dangerous.
They were different from the demons who were chaotic and only knew destruction.
Demons were evil by nature, but they would abide by the order and rules that they believed.