Makhleb
Makhleb: God of Destruction
At a time a full layer of Pandemonium was filled completely with Pain elementals, Chaos elementals and other experimental elementals created by a wizard trying to perfect his magic to create elementals and golems out of anything. In a particularly horrible miscast, the wizard merged himself into a pain elemental. As an intelligent being literally made out of suffering, constantly being tormented himself, but growing because of the suffering, instead of dying like a natural being would; his mind nearly broke; but barely, he was able to maintain his intelligence. In time; he began to see pain and suffering as a form of enlightenment, keeping his mind free and nimble from desires of comfort and luxury.
By inflicting pain and absorbing the suffering of others that entered his realm of Pandemonium, he grew; until he completely absorbed his previous creations; his wizard tower and several complete realms of Pandemonium. With his power, he developed tentacles into other dimensions, including the Abyss and the main world. He corrupted people driving them mad with torment to cause them to create temple in his honor and worship him. To any traveler, he offers his help in return for their constant emotional and physical torment; hurling bolts of chaos into their world in return for their pain. In truth, both the destruction he causes and the suffering of his followers allow him to grow in power.
He chooses to force people to hurt themselves in order to call upon his power to be certain that they are certain; in other words, as powerful as he is, he isn't omniscient, the eyes and suffering of his followers call his attention and his help is determined by their intelligence not his own. His destroying agents know that when they will die, they will merge with their god in eternal blessed agony forevermore. Makhleb, himself, knows that as long as nothing powerful enough (such as another god) tries to destroy him and people keep asking him for power, eventually he will absorb all of pandemonium and perhaps even a stake of the much disputed natural world.
When wandering pan, there is a chance you may find yourself inside of Makhleb. It's best to just find a portal to leave; as you cannot destroy him. Any pain you inflict upon him, may cause minor physical damage, but only serves to make him stronger. You'll know you are inside him, by seeing pained eyes in the walls watching you; perhaps marking you to send his servants to attack. Perhaps if you are strong enough, he could even attack you himself, thrusting tentacles inside himself to thrush you out and force you to become part of his gigantic flesh, made of the pained bodies of others that wandered into his domain and his former 'followers'.