Darkel

Inquisitor Darkel was a Time Lady who served on the High Council of Gallifrey. She presided over the Doctor's trial on the Time Lord Space Station Zenobia, with the Valeyard acting as prosecutor. (DW: The Mysterious Planet, Mindwarp) The Doctor himself would at a later stage act as his own defense lawyer. (DW: Terror of the Vervoids) (The Valeyard himself, apparently an independent Time Lord represented a dark side of the Doctor's personality.)

An honest woman, Darkel presided over a show trial designed to draw attention away from the corrupt High Council. With political unrest demanding a new Lord President and the Doctor unwilling to take on the job himself, he gave a symbolic vote of confidence to Darkel himself before departing in his TARDIS. (DW: The Ultimate Foe)

Behind the Scenes
During her on-screen appearances, Darkel had no name given to her, other than "the Inquisitor". The name Darkel was given to her in spin-off media (the canonicity of which is unclear. It has also been speculated that The Inquisitor may have been a regenerated Flavia.