The Raven Queen

The Raven Queen was once an especially powerful mortal (there is no mention of her original race in canon), who was either a powerful sorcerer-queen (who was also one of the first humans who learned magic directly from Corellon) or a mighty warrior, who died during the Dawn War (the ancient battle between gods and primordials during the creation of the cosmos). The cause of her death is conflictive in canon. She either died fighting in the war, or was a victim of one of the plagues unleashed by Nerull during this period of time. Regardless, fearing Nerull's actions and his ambitions to become "the King of all Gods", Corellon and Pelor, with aid of Sehanine and Moradin, strengthened her soul with more qualities than she had possessed in life: magical might, intellectual brilliance, shrewd discernment, unshakable courage, cold allure, and colder pride. This was done for Nerull to have a plaything to waste his time instead of trying to kill all mortals or follow his ambitions of being the King of the Gods.

So, Nerull took the bait: the soul enthralled him to the point he could not think in other stuff. So, he gave it a form and made her his queen. He called her "Nera" (this is not her true name, just the name Nerull gave to her after giving her a new form—her true name is forgotten and perhaps forever lost). Although "Nera" wanted nothing with Nerull, she was ambitious (perhaps a side effect of the strengthening of her soul?) and wanted to get Nerull powers for her, so she accepted his advances. Some say that Vorkhesis, the first of the sorrowsworn, is the fruit of this union (that maybe was born as a consequence of Nerull's... non-consensual advances on her).

During the final stages of the Dawn War, "Nera" finally was able to understand Nerull's ways to obtain power from the souls of the dead, and fed those souls, gaining immense powers. So, she fought against Nerull when the god was at his weakest (after a gruesome battle between Nerull and a primordial known as Athuam the Falling Sky) and killed him, absorbing his divinity. The other gods (who allowed this to happen, as they wanted to get rid of Nerull), fearing the appearance of a second Nerull, immediately moved and forbid her to take the portfolio of the dead, seeing the way she used the souls of the dead to kill Nerull. Thus, she was able only to become the goddess of death but not of the dead. She said that this was unjust, because she was unlike Nerull, and that soured her relationship with the other gods ever since.

Not long after, she made great efforts to circumvent this prohibition, like leaving Pluton to live in the Shadowfell, or expunging her true name from the cosmos, calling herself the Raven Queen from then on. She also sealed Nerull's holiest temple in a domain of dread, so Nerull cannot return to the world of the Nentir Vale (as Nerull still exists in some form—ie. its incarnation in the world of Oerth).

The Raven Queen, however, was able to get more power than the portfolio of death, thus becoming a major power in the Nentir Vale world. She aided Corellon in his battle against Lolth, and was able to stole Lolth's portfolio of fate, thus becoming known also in the Feywild as the power of destiny. And, in the War of Winter (a conflict that confronted god against god a few "years" —in god's reckoning— after the Dawn War) she asked over the porfolio of winter, that was the purvey of Khala, the original goddess of winter, as her payment for helping the gods to kill Khala. This was done because the Raven Queen was the only deity who knew how to kill gods in a way that they cannot easily return to life.

A few races believe they owe their existence to the Raven Queen. Kenkus believe themselves her first creations. According to their myths, her first action after her ascent to godhood was to ascent normal ravens, transforming them in kenkus (this myth plays an important role in the novel "The Last Garrison"). They also believe they lost their ability to fly because they lost her favor when they turned to revere the demon lord Pazuzu, dividing kenku society into those who revere the demon lord and those who revere the Raven Queen.

The shadar-kai descent from her first human worshipers. According to this myth, when the Raven Queen was still a new denizen of the Shadowfell, a tribe of humans known as Shadar Kai approached to her and proposed a deal: they promised to serve as her mortal agents, and in exchange, they asked for incredibly long life and freedom from frailty. The Raven Queen accepted, and the tribe went to live in the Shadowfell, where they evolved in the race they are today. Their tribal name became the race's name when they interacted with people from the mortal world again.

The sorrowsworn are all ascended shadar-kai, that gained this status after doing great deeds in her service.

The revenants, as well, owe their existence to the Raven Queen, as she uses them as her agents in the mortal world.

The vryloka (living vampires) also believe that was one of her aspects, the Red Witch, the one who gave them the blessing of being vampires without the taint of undead.