Keepers of the Realm
The name of the god of death is long forgotten, but she is called the Raven Queen. She is the spinner of fate and the patron of winter. She marks the end of each mortal life, and mourners call upon her during funeral rites, in the hope that she will guard the departed from the curse of undeath. She expects her followers to abide by these commandments:
✦ Hold no pity for those who suffer and die, for death is the natural end of life.
✦ Bring down the proud who try to cast off the chains of fate. As the instrument of the Raven Queen, you must punish hubris where you find it.
✦ Watch for the cults of Orcus and stamp them out whenever they arise. The Demon Prince of the Undead seeks to claim the Raven Queen’s throne.
"Other than Vecna, she is the only known deity who attained divinity after her mortal death".
When the gods first gained power, it was the evil god Nerull (The Reaper, the Foe of All Good, the Hater of Life, and the Bringer of Darkness) who took the domains of Slaughter and Death. He manifest the divine domain of Pluton (The Grey Waste) in the Astral Sea where he trapped the spirits of the dead if they were not claimed by their gods, and some that were. Here he served as his own form of judge over them, punishing them with terrible torment and using them for his legions. He found power in the armies of the dead and sought to reign over the other gods, in doing so he sent curses and plagues against the world, swelling the number of dead and the number of his legions. During this dark period the Fates found a mortal woman, a Sorceress-Queen of her people, and brought her into Nerull's grasp. He attempted to bind her and to make her his consort, but she spurned him. In time she found how Nerull kept the souls in his thrall and released them all, gaining power with each released soul while Nerull suffered. This gave her the power to conquer Nerull, take his divinity into herself, and become the Goddess of Death. The other gods were still rattled by Nerull's power and invoked the sorceress' True Name to bind her magical power, in a bid to protect themselves from anyone regaining the strength of the dead god.
The sorceress-queen used what magic she had remaining and hid her True Name from the cosmos later took the name The Raven Queen (The Reaper, Death, The Black Eyed Lady, Mistress of Darkness), gained power over the season of winter (The Ice Queen, She who Slumbers), and eventually joined the Fates (The Guide, the Hand that Weaves, The Cutter of Life's Thread). With her powers she established the city of Letherna as her kingdom in the Shadowfell, the new land of the dead and destroyed Pluton. She walked the mortal world for a while, guiding spirits to the Shadowfell and leaving waystones for the spirits to follow so they do not lose their way. She left the world on the Day of Passing and resides in the Shadowfell, guiding spirits on their journey from the mortal world through The Veil and into the Great Beyond.
After Nerull's death his angels found new gods to serve, most chose Grummsh (The One Eye'd Orc) or Torog (The King Who Crawls) to continue their slaughter while others joined with the Raven Queen, Asmodeus (The Ruby Tyrant), Orcus (the Demon Prince of Undeath) or Lolth (the Demon Spider Queen).
The Arcane Well
After the Raven Queen warded away her True Name she found that the gods still did not trust her. As a powerful sorceress with deific power, power over death and a member of the Court of Seasons no less, she was feared and plotted against. Seeking to quell the tension the new goddess agreed to give up her sorcering ways, but unbeknownst to the gods she didn't forfeit her powers, merely hid them in the Arcane Well. The gods of magic would know if she were to use her power and so the Raven Queen waits for a day when her power may be needed, when the other gods will become more trusting, or when they become less observant. Worshippers of the Raven Queen have scoured the East Continent but have found nothing. Many believe it must exist in the Western Continent.
Each creature in the universe is tied together in the strands of fate and the pool of life from which all creatures spring. Just as humans have a name, each creature also bears a True Name, or a Fate-Name. These names reference the being at a cosmic scale and offer control over them when invoked. A True name is a powerful thing, but also fragile. Each True name is rendered as a compilation of events in the creature's life, from the tree it passes while walking to the food it eats or who it takes as a mate. Invoking a True name may grant you control over the creature for a short term, but it will also change the True name rendering the original worthless. The Raven Queen does not reveal True names to mortals unless they have received her blessing. Those who seek the Raven Queen's own true name are stonewalled or killed in strange and horrible ways.
Mainly the Shadar-Kai and some followers of the dark arts.
The Sorrowsworn are servants of the Raven Queen, angels of death, and reapers of souls. They journey to the material plane and collect the souls of the dead that are unclaimed by other Gods. After harvesting the souls, they bring them to the crypts of Letherna were the souls rest for eternity. When they are slain, they vanish into wisps of black smoke only to be reborn in Letherna some time after.