Arden-Sul was a powerful prophet and ruler from an old time in the Shivering Isles. The events of his life and death are widely disputed by the people of the Isles, particularly in regards to the Sacellum. As with everything else in the Isles, the division in viewpoints lies between Mania and Dementia. The only thing the ruling powers seem to agree on is that he was a prophet who preached in the building that shares his name, the Sacellum Arden-Sul and had 213 followers. The Manic and Demented versions of his death have even become part of the ritual of accession for each respective duchy. A longer version of his life can be found in the book The Prophet Arden-Sul. Not much is known about Arden-Sul. Some say he was a hero, some say he is some sort of god. The Heretics believe that Arden-Sul is the true lord of the Shivering Isles and that Sheogorath is just a man who needs to be overthrown. The Zealots believe that Sheogorath is a living god (an Aedra bound in human form) and that Arden-Sul is the personification of Sheogorath's mortality. The beliefs of the maniacs and the demented contradict each other almost completely.
As the Manic and Demented are always fighting about what is to be considered good and bad, the belief of his life and death is told by each high priest in the Sacellum, and differs by each shade of madness. For instance, the Manics believe he was an abstract thinker, writer and artist, an all-in-all blissful man who loved lavishness and over-indulgence, much like the Daedric Prince Sanguine whereas the Demented view him as a dark, distrusting, and a traitorously deceptive web-weaver more like the Daedric Princes Boethiah, Mephala, Namira, and Vaermina. To the Demented an all-in-all violent and murderous person is considered good. The different beliefs of his teachings are told in the Sacellum, depending on which faction is in power.
In the Manic tradition, Arden-Sul had a party at the Sacellum that became a massive night of indulgence. Greenmote, wine, dancing, poetry and all pleasures of the flesh that the Manics love was folded into one night. At the climax of the party all 213 of his guests dropped dead, their hearts literally having burst from an overdose of the potent drug greenmote. Arden-Sul was reportedly the last to die and was in a state of great bliss. Now, when the Duke or Duchess of Mania feels it is their time—or sometimes when the successor takes it upon themselves—they invite their successor-to-be to a grand feast and the current duke will partake of an overdose of Greenmote, causing their own death. The former duke's blood is then taken to the Sacellum, and the successor is made Duke of Mania.
In the Demented tradition, Arden-Sul feared his followers as potential traitors and went searching for a way of knowing a person's true feelings. Eventually, he discovered visceromancy, the science of divination through the observation of the entrails of others. Summoning his flock to the Sacellum, he poisoned the wine, leaving his followers paralyzed. He then cut out their hearts in order to find the traitor. Angered by his failure to find one, he tore out his own heart, only realizing as he died that he was the traitor, destined to kill himself. Unlike the Manics, the Demented succession customarily involves murder of the predecessor as murder and betrayal are respected themes in Dementia. The heart of the former duke is taken to the Sacellum, and in a similar fashion to the Manic ritual, the successor is made the new Duke of Dementia.