From the Irish bean sí or bean-sidhe, banshees are the spirits of elven women tormented by grief and betrayal. In folklore, a banshee’s keening is sometimes even said to foretell death. Given the deadliness of her wail, she is also likely to be the cause.
Laird Loark Elf-Friend gave his life to save the elven nation of Aspensong from a red dragon. His sons were promised that elf swordmaidens would guard his grave, and theirs, and those of his heirs, to ten human generations. Then plague wiped out twice-cursed Aspensong, but the vow held, and now banshees stand vigil over the Loark crypt.
Betrayal is a fact of drow life, so those dark elf banshees that do arise are not always as hopelessly enraged as their surface counterparts. A few matron mothers even relish their newfound status and powers, and pick up ruling right where their corpses left off.
An evil crystal artifact from the Plane of Earth can only be shattered by the wail of a willing banshee skilled in song (minimum bard 2). A copper dragon knows where one such spirit might be found—a lyrist slain by a shaitan’s scimitar.
—Pathfinder Bestiary 2 41