The Darksmith Agent was a tall, powerful and intelligent skeletal robot with a silver skull, beautifully crafted and used by the Darksmith Collective to recover the Eternity Crystal after it reappeared on the Earth's moon and was taken by the Doctor.
It was a product of Darksmith technology and a masterpiece of engineering, programmed with an innate understandings of the Time Vortex (found in a deactivated Gundan robot), allowing it to travel on the time winds. Its metal bodywork was augmented with plastic salvaged from the wreckage of the Nestene homeworld, Polymos. Its internal mechanisms were visible through a transparent outer layer, its photothermic vision allowed it to track body heat, and its brain was a computer core matrix which shared the same crypto-molecular structure as the Eternity Crystal, a product of former-brother Varlos of the Darksmith Collective. (PROSE: The Dust of Ages)