The Ideal Masters are mysterious entities that lord over the Soul Cairn, controlling every aspect of its reality, similar to how a Daedric Prince does with their plane of Oblivion. They are an enigma to the inhabitants of Tamriel, and only those who make deals with them or have visited the Soul Cairn know of their existence. Most individuals who deal with the Masters are deceived, and subsequently their souls are stolen. While there are theories, exactly why the Ideal Masters crave souls is unknown.