Description of Nimue (The Blood Queen):

Nimue lived during the reign of King Arthur, and was beloved by Merlin, who told her all his secrets. She used this knowledge to imprison him in a grave for eternity. But without Merlin to guide her, Nimue's knowledge of magic drove her to madness and eventually to worship the Ogdru Jahad. Also known as "the Queen of Blood" or "the Lady of the Lake," was the greatest of all British witches.