Dyus was the former keeper of the Great Library of Jyggalag as well as Jyggalag's trusted Chamberlain. Within the library was all the knowledge of creation, consisting of logical predictions of the actions, events and deeds of all sentient lifeforms (creature, mortal and Daedra) in existence, that previously existed, and would ever exist, using the logical formulae found within the library.
When Sheogorath was born from Jyggalag's curse, and discovered the Great Library, he had the knowledge burned and the library destroyed, seeing it as an abomination as he viewed that personal choice surpassed logical prediction. Sheogorath destroyed everything except for Dyus, unable to bring himself to destroy the knowledge he possessed. To prevent others from locating him and using his knowledge with ill intent, Sheogorath imprisoned Dyus inside Knifepoint Hollow and granted him immortality, making sure that he wouldn't die within his prison.
Haskill recommends that the Hero see Dyus at Knifepoint Hollow. Dyus will tell that the Eye of Ciirta and a branch from the Tree of Shades are needed. Once both items have been collected, return to Dyus. He will create the unfinished Staff. He then says to travel to the Tree of Madness in Sheogorath's throne room and tap the Tree's power to complete the staff.
Dyus portrays himself as a reserved individual, whose immortality and eternal imprisonment are of no bother. To him, individuality is an illusion, and he considers his own life and existence is just about as important, in the long run, as the entire history of a stone. Despite believing this, he will still answer questions about his past. He also considers space and time as artificial concepts, used by men of baser intellect to make sense of the world, and states that only a few fortunate minds can see past this convention.
Due to his knowledge of Jyggalag's logical formulae, he is said to possess knowledge of every event to ever occur. If asked about him, Haskill will mention that Dyus knows things that even the Daedric Princes do not know, making him a powerful individual. However, due to his determinism, he considers these events and their occurrence as unchangeable and certain, and does not attempt to interfere. Those who believe in personal choice, however, such as Sheogorath and Haskill, consider this idea "debatable." He also does not seem to discriminate as to who he will give knowledge to, as he helped the Hero gain the means to defeat his old master, despite predicting certain failure.
Despite his determinism, he incorrectly predicted that the Hero would not be able to acquire the ingredients for the Staff of Sheogorath. When he discovered this, he was somewhat surprised, and expressed that he was now uncertain of the Hero's fate, though he immediately attributed this to an error in deduction on his part. After completing the questline and returning to him, he will state that he loathes the concept of personal choice, as it makes things imprecise. When asked about his imprisonment, he states that he knows when the new Sheogorath intends to finally free him, and asks for the Hero to leave them be.
- The place known as Mytheria is not mentioned anywhere in the lore, besides that Dyus originates from this place. What and where it is has not been revealed, but the common assumption (though an assumption it still remains) is that it was the name of the Shivering Isles in the time of Jyggalag's reign there.
- If this interview of Dyus and Haskill is to be considered canon, then it shows that Dyus himself does not actually remember if Mytheria is actually real, believing it was either removed from his memories by Jyggalag, or that the idea of it was simply implanted by Jyggalag.