Cloister Wraith

The Cloister Wraiths were creatures found in the Cloisters, a crypt beneath the Capitol of Gallifrey, and were often referred to as ‘Sliders’ by the Time Lords.

The Cloister Wraiths were representations of dead Time Lords whose minds had been uploaded to the Matrix – a living Gallifreyan computer – designed to guard it, much like a firewall. The Matrix was capable of predicting the future, generating prophecies out of algorithms and ringing the Cloister Bells of Gallifrey in the event of impending catastrophe.

With the Doctor’s return to Gallifrey, the Cloister Bells were heard all across the planet, and the Cloister Wraiths became very active, but most Time Lords were too afraid to enter the Cloisters properly. As the Doctor and Clara later discovered, anyone known to have entered the Cloisters, including powerful aliens determined to steal the Matrix’s database secrets, were attacked and ‘filed’ by the Wraiths, trapped forever. Only one individual, a student of the Time Lord Academy, was rumoured to have escaped the Cloisters and the Wraiths, by finding a secret passage. As Clara discovered, this individual was the Doctor. His knowledge proved useful, when both she and the Doctor were forced to flee into the Cloisters to escape the Time Lords.

The warnings of the Cloister Wraiths were proved correct when the Doctor’s course of action in trying to save Clara threatened to be responsible for the very devastation of Gallifrey that the prophecy of the Hybrid had warned of. (TV: Hell Bent)