Hermaeus Mora

Hermaeus Mora, also known as Hoermius, Hormaius, or Herma Mora, is the Daedric Prince of knowledge and memory; his sphere is the scrying of the tides of Fate, of the past and future as read in the stars and heavens. While his alignment is largely unknown, he seems to be the keeper of both helpful and destructive knowledge.

Background
Unlike most of the Daedric Princes, which usually must be contacted via praying at a shrine, Hermaeus Mora may appear intentionally at an individuals' presence without summoning. When confronted, he usually takes the form of a large mass known as the "Wretched Abyss" that consists of tentacles that spread out from a large eye located at the center of the mass. His personality is noted to be rather calm, even when the individuals defy or defect his requests.

Hermaeus Mora governs a plane known as Apocrypha, in which forbidden documents and knowledge is known to be stored at. The realm behaves as though it is an endless library, with endless stacks of books and scrolls, some of which defy the laws of gravity and physics. Besides Hermaeus Mora, other entities inhabit the plane, notably Seekers gathering and guarding knowledge, Lurkers, which sometimes appear outside of the plane, and various ghosts seeking the knowledge they wished they had found in life. It is also the makeshift home of the First Dragonborn Miraak and his dragon henchmen.

The Elder Scrolls V: Skyrim
Hermaeus Mora first appears after the Dovahkiin accepts a mission given by the crazed mage Septimus Signus to gather blood from all living Mer (Elf) races in order in purify into Dwemer (Dwarf) blood in order to open a vault located in the cave Signus dwells in, which he thinks contains the Heart of Lorkhan. Hermaeus Mora appears towards the exit and tells the Dragonborn about what is actually behind the vault: a tome known as the Oghma Infinium, personal daedric artifact of his. He also states that while Signus was useful, his usefulness has since run out and that he will deal with his fate soon enough. He then allows to the Dragonborn to carry on with Signus's request.

After finally obtaining every sample of Mer blood, Signus unlocks and opens the vault door and becomes shocked to see that the vault's contents is not the Heart of Lorkhan, almost immediately he then combusts into ashes, seeming as though Hermaeus Mora has sealed his fate. The daedric prince then appears in front of the Dragonborn and declares him his new champion, before allowing them to seek the knowledge held inside the tome.

Hermaeus Mora makes his second appearance in the Dragonborn DLC. Here, it is revealed that the First Dragonborn known as Miraak was once a champion of the daedric prince of knowledge, but soon when rogue and exploited the forbidden knowledge for his own personal and evil needs. Being dumbfounded, Hermaeus Mora seeked vengeance on the traitor since then.

Upon obtaining a black book, the Dragonborn travelled to Apocrypha where they met Hermaeus Mora once more. Should they have obtained the Ogham Infinitum, he will immediately recognize them as his champion and make them an offer. In exchange for seeking the endless and forbidden knowledge of his realm without incident, Herameus Mora demands they defeat Miraak for his traits actions against him, but in order to successfully defeat him, the current Dragonborn must learn the words to a shout known as Bend Will, while the first two words are obtained easily, the third must be obtained after seeking the wisdom from the Skaal tribe by means of the tribe's shaman Storn Crag-Strider.

After successfully obtaining the third word of power, the Dragonborn travels back to Apocrypha to confront Miraak. After a long battle, the Dragonborn ends up having the app hand until Miraak attempts to avoid death by escaping the waters, however he for he is able to do so, Hermaeus Mora appears and impales Miraak before draining his soul and distributing it to the Dragonborn. He then grants the Dragonborn Mirk's status and thanks them for fulfilling his request.