Originally nine mortal humans, they succumbed to Sauron's power through wearing the Rings of Power, which gave them immortality and worldly power at the cost of eventually reducing them to invisible wraiths bound to the power of the One Ring and completely under Sauron's control; this is the...
(Example: In ALttP, Death mountain is Northeast of Hyrule castle. In OoT, Death Mountain, although in front of Kakariko, is still Northeast of Hyrule castle as seen from the Temple of Time's infamous view of the flaming ring above the Death Mountain Crater). In Wind Waker, it is rather...