Castellan

The unnamed Castellan of the Time Lords was responsible for helping the Doctor seal the Vultures in the Quantum Ark, but subsequently neglected to improve its technology to keep them locked in there.

Character History
It is unknown at what point in his life the Castellan was handed his title, but he served alongside the President during the Vulture crisis. The Castellan wanted to ensure the Vultures' death so as not to risk the future of Gallifrey, but was forced to comply with the Doctor's wishes when he persuaded the President to allow him to imprison the Vultures in the Quantum Ark. He and the Doctor took the Ark to Titan 6, where it was left, and the Castellan was charged with improving the technology so as to make sure the Vultures wouldn't get out. He did not do this however, dying before he could make advancements to the Ark.

Season 1 (2015-2016)

 * 1) The Sins of the Time Lords