Sepulchra
Sepulchra was a Time Lady encountered by the Eighth Doctor and his companions onboard an ancient TARDIS they found floating in the vortex.
Originally a tutor at the Time Lord Acadey on Gallifrey, she taught a young Caleera in her classes, but had little tolerance for the student's propensity for getting distracted and tuning out of her lectures. She did however see that Caleera was a "bright girl", but had no patience for her daydreaming. She was present when Caleera sufferred an episode due to her burgoening psychic abilities, and was injured, though not seriously. Caleera bore a grudge for years, and after she was manipulated by the rogue Time Lord known as the Eleven, she used her returned abilities to punish her. She then recruited her along with two other Time Lords to act as helpers in her efforts to expand her abilities even further.
By the time the Doctor arrived, she had taken to calling herself "Lady Sepulchra", and had been slowly driven mad through exposure to the time winds, since the TARDIS had badly degraded, loosing it's outer shell completely. She remembered enough to still help with the experiments, and that it used Caleera's own psychic powers. Once Caleera was free, she lowered the TARDIS shields, allowing Sepulchra and her companions the death they longed for, sending them falling into the vortex. (AUDIO: Scenes From Her Life)
