Castellan Aulric is a Timelord from Gallifrey and an old friend of the Tangent Doctor's.
He is a Timelord of the Petrexes Chapter and wears flamboyant heliotrope robes. Aulric is quite liberal-minded to other chapter houses, although he regains a sense of duty and secrecy to all matters concerning the high council. He is also very good "friends" with the president of Gallifrey, Logelious. It is unknown what their past relationship was like, although the creators of the series claim it to be a homosexual one.
It is also hinted that he had a past, but brief relationship with the Doctor at some point.