Ostrev
From Tardis Wiki, the free Doctor Who reference
Ostrev was a Time Lord, modified to resemble an Elder Thing for camouflage, during the War in Heaven.
Part of Xenaria's mission group to free the Fendahl from the time looped Planet 5, Ostrev was killed by Investigator One during a psychotic episode induced by shock and paranoia brought upon by the Eighth Doctor's worldview of the Swimmers. (PROSE: The Taking of Planet 5)