As the opposite force to the White Guardian - Guardian of Light and Time - the Black Guardian is the Guardian of Darkness. The Guardians are beings of immense power. Neither the White Guardian nor the Black Guardian can exist alone, as the two of them together maintain the balance of the Universe. They will exist until they are no longer needed.
The Black Guardian cannot be seen to act in matters directly, so he always uses a servant - Cessair of Diplos, the Shadow, Turlough and Wrack, to name a few. He may use a crown-shaped crystal to communicate with his servants; it is held in the hand and glows when the Black Guardian and his servant are communicating. The crystal can attach itself to the hand, to prevent its being discarded, or it can be used as an instrument of pain by the Black Guardian. It may crack if the Guardian is displeased, but will repair itself; and if the Black Guardian's contract with his servant is terminated, the crystal will blacken.
The Black Guardian can appear to people physically, as an image or in dreams. He can channel his destructive power through the mind of his servants to a focal point. And he never, ever accepts failure. If his servants fail him, he will likely abandon or kill them. He himself cannot be killed, of course, but he can be thwarted.
