Pandora

From TARDIS Index File, the free Doctor Who reference.

Pandora was an ancient female Time Lord that existed early in Gallifreyan history and was the first female leader of her people.

According to legend, she decided to lead Gallifrey to war and attempted to use the power of time travel to reshape the Web of Time to suit her own design. She was also known to have taken an offworld bodyguard who killed all those that opposed Pandora's will. In time, however, the High Council managed to convince the bodyguard to betray her master on the condition that the Time Lords would help improve her people's livelihood. However, once Pandora was betrayed, the High Council took the bodyguard back to her planet where she was placed in an eternal 6.8 second time loop from which there was no escape.

The captured Pandora was dispersed and executed in such a thorough manner in that she never existed in the first place. This was why she existed only in legends and not in history. The dispersal chamber itself was located in the old Capitol where it was destroyed in Gallifrey's civil war. The new Capitol was built over the ruins which became the Vaults. The legends said that Pandora's dying screams still could be heard in the Vaults where she eternally cries out for vengeance. (BFA: Lies)