Demogorgon, The Sibilant Beast

History in the Abyss is utterly useless, nonsensical... How can one actually document the history of the Deepest Well in the Timescape, where time and space folds in upon itself in the most maddening ways? It's impossible... Yet some aspects of what has happened, and what will happen do exist, and hold some weight in this Realm. Even in a Realm such as this, there is a beginning, there is an end, there is a Last, and there is a First...
Demogorgon was that First...
The Obyriths may have pushed Tharizdun to create the Abyss, and they may have been the first to cross over and dwell there, but they were not the First True Demons. They were... Guests... No, Interlopers... An Infestation... And soon they would learn that the Realm of the Abyss could only belong to those birthed by it.
After Tharizdun was locked away, and the Obyriths claimed dominion of the Abyss, new beings formed from its essence. Some the souls of the first mortals, some beings shaped by the Abyss itself. The first form the Obyriths came across was hideous. A writhing mass, deformed and screaming and Mad. An abomination unworthy of existence. And so it was cast aside, left to die while others rose, fell, ruled and conquered. All while the abomination grew in power.
When the Obyriths fell, and power within the Abyss shifted, many fought amongst each other for the right to rule. Blood flowed like a river, souls sundered, many a Demon fell into Lethe... Dagon resisted the Lethe, Relg radiated it, all while Orcus's hordes Flooded the Abyss. No one expected the raw power, the ruthless cunning, or the Maddness incarnate that was Demogorgon, the First of his Kind. One by one, the others fell to him, until only he stood as Prince of Demons.