Vigil

The Vigil are a society of aliens from the Doctor Who universe and a trio of them acted as antagonists in the Rings of Akhaten, while in essence their goals can be seen as noble their willingness to commit murder and similar atrocities made them enemies of the Doctor.

Unlike many Who monsters the Vigil wished to prevent a greater evil from awakening in the form of the parasitic planet, Akhaten, yet in order to ensure the "god" would stay asleep they pursued and sacrificed an innocent child - when encountered by the Doctor three of these beings were working with the Mummy to capture and sacrifice one such child, a young girl.

This went against the principles of The Doctor, who wanted to prevent the senseless cycle of death as well as awaken Akhaten so as to confront the "god" and end its tyranny upon the planets - pitting the Vigil in battle against him.

Ultimately the Vigil lost as the Doctor succeeded in awakening Akhaten, believing their purpose to have failed the trio vanished, showing yet more callousness in the fact they were willing to leave all seven worlds to die the moment their cycle of sacrifice was disrupted.