"Thasaidon, lord of seven hells
Wherein the single Serpent dwells,
With volumes drawn from pit to pit
Through fire and darkness infinite —
Thasaidon, sun of nether skies,
Thine ancient evil never dies,
For aye thy somber fulgors flame
On sunken worlds that have no name,
Man's heart enthrones thee, still supreme,
Though the false sorcerers blaspheme.
-- The Song of Xeethra"
'The Dark Eidolon' (1935) by Clark Ashton Smith
Persia Parade shield sipar
Deep within the forsaken deserts of Zothique lay abandoned cities & half forgotten temple complexes to Thasaidon one of the last devil kings of Hell. The bloated red sun of Earth holds sway over all Zothique, Thasaidon holds court with the souls of black magicians & wizards from Aramoan to Zul-Bha-Sair. But where did this devil king come from?! The cold Outer Blackness or is he something far more sinister & familiar. He figures most prominently in 'The Dark Eidolon' (1935) by Clark Ashton Smith. Thasaidon is a devil king of business & black magick. He's in the business of the souls of mankind especially magicians & on Zothique business is very good. In 'The Dark Eidolon' we are given the internal view point between Namirrha Thasidon's pet arch wizard & the Devil King;
"Before the black-armored image there hung seven silver lamps, wrought in the form of horses' skulls, with flames issuing changeably in blue and purple and crimson from their eye-sockets. Wild and lurid was their light, and the face of the demon, peering from under his crested helmet, was filled with malign, equivocal shadows that shifted and changed eternally. And sitting in his serpent-carven chair, Namirrha regarded the statue grimly, with a deep-furrowed frown between his eyes: for he had asked a certain thing of Thasaidon, and the fiend, replying through the statue, had refused him. And rebellion was in the heart of Namirrha, grown mad with pride, and deeming himself the lord of all sorcerers and a ruler by his own right among the princes of devildom. So, after long pondering, he repeated his request in a bold and haughty voice, like one who addresses an equal rather than the all-formidable suzerain to whom he had sworn a fatal fealty.
"I have helped you heretofore in all things," said the image, with stony and sonorous accents that were echoed metallically in the seven silver lamps. "Yea, the undying worms of fire and darkness have come forth like an army at your summons, and the wings of nether genii have risen to occlude the sun when you called them. But, verily, I will not aid you in this vengeance you have planned: for the emperor Zotulla has done me no wrong and has served me well though unwittingly; and the people of Xylac, by reason of their turpitudes, are not the least of my terrestial worshippers. Therefore, Namirrha, it were well for you to live in peace with Zotulla, and well to forget this olden wrong that was done to the beggar-boy Narthos. For the ways of destiny are strange, and the workings of its laws sometimes hidden; and truly, if the hooves of Zotulla's palfrey had not spurned you and trodden you under, your life had been otherwise, and the name and renown of Namirrha had still slept in oblivion as a dream undreamed. Yea, you would tarry still as a beggar in Ummaos, content with a beggar's guerdon, and would never have fared forth to become the pupil of the wise and learned Ouphaloc; and I, Thasaidon, would have lost the lordliest of all necromancers who have accepted my service and my bond. Think well, Namirrha, and ponder these matters: for both of us, it would seem, are indebted to Zotulla in all gratitude for the trampling he gave you.""
Let's look at the ramifications of this conversation for a moment. Thasaidon is considered the 'Lord of All Turpitudes' among his royal titles of Hell. He's telling one of the most powerful black magicians of his generation to give up his revenge against the king Zotulla. One of the most powerful lawful evil devil kings is telling his summoner to give up this fool's errand. That's the gravity of the situation in 'The Dark Eidolon' . But who is Thasaidon himself? His identity is tied up in his titles Thasaidon is the 'ruler of the Seven Hells' & 'Lord of All Turpitudes'
Terpitudes is defined by the Merriam-Webster dictionary;
"The word is often heard in the phrase "moral turpitude," an expression used in law to designate an act or behavior that gravely violates the sentiment or accepted standard of the community. A criminal offense that involves "moral turpitude" is considered wrong or evil by moral standards. "
In Dungeons & Dragons there are the Nine Hells but sometime millions of years in the far future world of Zothique two of those planes are destroyed. Asmodeus is not only defeated but absorbed by Thasaidon. He emerges from the Chaos of this war to take his rightful place as one of the patron gods of Zothique.
How do I know this because Thasaidon is the 'Prince of All Moral Turpitude' & ruler of the Seven Hells. These are the planes of Hell that emerge at the end of Revelation & after the Horsemen have been released on Earth.
"Then I saw when the Lamb broke one of the seven seals, and I heard one of the four living creatures saying as with a voice of thunder, “Come.” I looked, and behold, a white horse, and he who sat on it had a bow; and a crown was given to him, and he went out conquering and to conquer.
— Revelation 6:1-2 New American Standard Bible (NASB)"
One by one the armies of Hell consume themselves & each other after the Fall of Man. Two of the planes of Hell burn away into the Outer Darkness. Asmodeus is the last to fall in battle & from his ashes will emerge Thasaidon. Each of Hell's sins is taken over by Thasaidon & he literally takes on the titles & reignments of Hell.
This war makes the Blood War look like 'Sunny Brook' farm & the struggle is epic. The souls of all mankind across the planes are at stake. And what's left is a very different landscape of Hell. The devil king of Zothique is a very different beast from Asmodeus & after the reforging of Asmodeus's ruby staff into the iron mace Hell becomes a very different place. This has happened many times in the past & the cycle will continue. The cults of Thasaidon have begun to spread among the outer fringes of the world today because of the prophecies that have been revealed among certain esoteric seers. These cults are violent & very dangerous. They should only be tackled by the most experienced of adventurers. There cliques of these cults that have emerged on Hyperborea as well but many consider these to be ancient relics of a bygone age today.