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You may be looking for the year 0 or Prisoner Zero.

Lord Cardinal Zero was a member of the High Council of the Time Lords. Like the Doctor, he was a Prydonian. He was a member of the Council of the Great Mother, and specialised in the politics of regeneration.

Despite already having the title of Lord Cardinal, the Fifth Doctor stated that Zero was only "well on his way to getting a seat on the High Council". (AUDIO: Spring)