The Raven Queen

Although a complete account of the Raven Queen's motivations and origins was not generally known, it was believed that she was originally a much beloved elf queen from the Feywild who witnessed the conflict between Corellon and Lolth. Worried that the dispute might tear the Seldarine asunder, she rallied her followers to perform a powerful ritual in order to become a deity, so she could have the leverage to appeal to the deities' senses.
The ritual involved the offering of the queen's followers' souls and magic to add to her own power, enabling her to reach Arvandor. The followers, who called themselves shadar-kai, firmly believed that their queen was capable of reunifying the elven pantheon and the sundered elves.
However, evil wizards among the queen's followers attempted to divert some of the energy from the ritual to amplify their own powers. Moments before completing the ritual and reaching Arvandor, the queen reacted by punishing the wizards with a burst of divine fury. This curse corrupted the ritual into a siphon that dragged the queen and her followers into the Shadowfell, where she was instantly killed. However, thanks to her recently acquired divine powers, the queen rose from the ashes and, in her growing madness and grief, transformed the wizards into wretched avian forms known as nagpas, and banished them forever to wander the planes.
The queen herself was still further transformed by the corrupted ritual, her form dissolving into disconnected sensory perceptions. Moreover, both Corellon and Lolth considered her actions to be treason, so they erased the memory of her existence from all elves. In order to avoid disappearing entirely, she drew memories of her existence from the Shadowfell itself in order to sustain her identity. Over time, the subjective remains of the queen and the loose darkened memories gave rise to the entity that became known as the Raven Queen.
At some point, Firble Gemcutter became a servant of the Raven Queen and allied with her in his bid to become the Lord of Shade.