Hells

The Hells is a plane of existence that was constructed to imprison Cemeris, the god of trickery and deception. It has several layers.

Creation
When Cemeris assumed the guise of Auris in order to manipulate the god's followers, she led them to commit the first acts of murder- and the first deaths in the universe. For this inexcusable crime, she and her loyal subjects (now known as devils) had a special plane of existence created just for them to be imprisoned in. This became known as the Hells.

Souls
Cemeris' trickery extended beyond her stay in the material plane. The hearts of all creatures were now consumed with violence and evil as much as they were with peace and goodness, and there was an abundance of death. With nowhere to go, the souls of the dead floundered around the material plane, and they became so thick that it led to the creation of the ethereal plane. The Supreme Divine decided the souls must go somewhere, and appointed a judge to sort the good ones from the bad. The bad ones were- of course- sent to the Hells.

Cemeris wasn't particularly fond of this, so she locked herself and her loyal devils away in a black fortress at the edge of the Hells. The souls that arrived in the Hells, evil and twisted, entertained themselves by torturing each other and rarely ever wandered to her corner of the plane. They tortured each other into submission, and the Hells was soon a writhing mass of agonized souls each vying for dominance, which they never kept for long. Still, Cemeris kept a watchful eye.

The Demon Wars
When Covinex was sent to the Hells for creating and leading his murder worshipping cult (as well as his own mass-murder), it was assumed he would fall victim to horrors of the Hells as much as the next soul. However, much to the misfortune of everyone, he enjoyed it. Covinex quickly proved himself to be the dominant soul in the Hells, and he tortured many souls into following him. These souls, blackened by pure evil, were twisted into demons.

Cemeris' paranoia proved to be warranted. Soon the masses of demons led by Covinex seemed to be casting their eyes towards her corner of the plane. She wanted them out. To do this, she made a deal with an apprentice of Arimikos. A young upstart mage who had been cast aside by his mentor, he was eager to take power from another source. As part of the deal, at the peak of his power, he was to open a gate to the Hells. When he accepted he became the first warlock.

When he held his end of the deal and opened the gate, Covinex' attention shifted to a grander prize- the material plane, and hordes of demons swept like a bloody, fiery wave across the land. When they were all gone, Cemeris closed the gate off behind them, but not before sneaking a few of her loyal devils onto the material plane.