The Daughter of Khyber, also called the Tyranny of Dragons, is one of the Overlords who ruled over all of Eberron during the Age of Demons. She was bound by the dragons and couatl after they jointly discovered the Draconic Prophecy, and the couatl sacrificed themselves to form the Silver Flame.
The Daughter of Khyber is thought to be the closest of the Overlords to their progenitor, Khyber. She is the incarnation of the evil that resides within the heart of every dragon, the potential for unchecked ambition and the domination of the "lesser races". Every time a dragon interferes with events in the wider world, altering the direction of nations or the history of the world, she grows more powerful.
She is bound within the Pit of Five Sorrows in Argonessen, where she whispers to and corrupts her draconic jailers. Dragons volunteer to guard her prison, knowing full well that they will be executed at the end of their tour of duty to prevent them from falling to her corruption, they know they are preserving the world.