Whispers nagging pleading demanding advising ignoring prattling mocking...
Always whispering. Thousands, millions of voices whispering.
Sibilant whispers.
Demogorgon is plagued by them. He/they have always been.
One voice calls itself the Slave, and rages over its long-ago captivity in the jaws of the god Sekolah.
One voice calls itself the Child, and mulls over the destruction of the multiverse, making piping sounds sweet as honey.
There's the Queen of Darkness with her reptillian hordes, the Elder Kraken with its unspeakable lusts, the Furies with their endless cries for vengence, Demos the Creator with his self-importnat servants, and Gorgos the Monster with his hatred of all that is.
Many of the voices have an inexplicable fear of the serpent god Merrshaulk.
But Demogorgon has finished out what to do with them: to rid himself of the whispers, all he has to do is build them worlds.
And he's figured out how. At least, some of the voices have. Deep within the fortress Abysm the fiend draws forth the energies of the Abyss and shapes them into entirely new layers. He's already made hundreds.
If some abyssal lords were to know about this plan, they'd scoff. What's the use of dividing infinity? Any one layer of the Abyss is already plenty large enough to hold all the demons that ever were and more besides - Demogorgon should be looking outward to expand his holdings toward the layers of other lords or parts of other planes, rather than weaken his own.
But some of Demogorgon's more lucid voices know what they're doing. A layer of the Abyss can be many things, among them a laboratory for the creation of new tanar'ric breeds. He's made others into plane-crossing ships, or just hidden them away. There are half a dozen in chests stashed in his towers and vaults. He put one inside a gemstone and gave it to a shadow-fiend.
The vast majority of Demogorgon's infinities are unknown and uncatalogued by anyone. Others he busily fills with tanar'ric recruits, or ships to special locations. What would happen if the Abyssal layer he froze in Caina's ice were to thaw a thousand thousand years from now? Perhaps a specially timed fireball would ensure that...
Relations: it's said that the monkey-headed Abyssal prince Mandrillagon is either Demogorgon's brother or son. In fact, Mandrillagon is another of Demogorgon's voices, somehow given his own flesh - possibly made from an entire layer of the Abyss, collapsed into a humanoid form. Mandrillagon rules a layer filled with bar-lgura, quaggoths, and rakshasa. He doesn't like Demogorgon much, but will ally with him in times of crisis.
Merrshaulk: the myths of the dragons, nagas, and couatl tell of the World Serpent, an archetypal being that supports, creates, destroys, and recreates the multiverse. Different aspects of this being have different levels of purity or debasement - the dragons call their most favored aspects Io and Io-Chronepsis, while the couatl call their most revered aspect Jazirian.
Both races agree that Merrshaulk is the most corrupt and hateful aspect of the World Serpent imaginable, too torpid and useless for any proper entity to revere, but it just might in some sense *be* the Abyss incarnate (as the couatl believe Jazirian is the incarnate form of the Seven Heavens). If this is true, all other serpentine entities of the Abyss, including Demogorgon, might be a further corrupted form of *it* -something like a dream imagining it was the dreamer. What would happen were Merrshaulk to fully wake? Would all the layers of the Abyss merge into one?
Perhaps better not to speculate.