Dæmos

Dæmos was a planet roughly sixty thousand light years from Earth, on the far side of the Mutter's Spiral. The Dæmons were from this planet. (TV: The Dæmons) Like a million other worlds "right across the universe", Dæmos had "the representation of the horned beast" in its myths and legends. The Beast claimed to be this "devil", along with all of the others in every religion which had such a figure. (TV: The Satan Pit)

Behind the scenes

 * Philip Purser-Hallard's T.memeticus: A Morphology features the (unnamed) Daemons, and establishes that their world is the Infernal Sphere, a Dyson sphere built around a black hole. It is unclear if this means Daemos is completely separate, exists within the Sphere, or is the Sphere.
 * Simon Bucher-Jones' Doctor Who and the Exile from Hell, published in A Second Target for Tommy, features the version of the Daemons seen in T.memeticus: A Morphology, and implies that Daemos and the Infernal Sphere are one and the same.