The Ultimate Foe

The Ultimate Foe is the fourth and final serial of the larger narrative known as The Trial of a Time Lord which encompasses the whole of the 23rd season of the British science fiction television series Doctor Who. It was first broadcast in two weekly parts on BBC1 on 29 November and 6 December 1986. This segment is also cited in some reference works under its working title of Time Incorporated (or Time Inc.). The title The Ultimate Foe is never used on-screen and was first used in relation to these episodes for the 1988 novelisation, with the two episodes that comprise the serial being referred to as The Trial of a Time Lord Parts Thirteen and Fourteen. This was the last story to feature Colin Baker as the Sixth Doctor, as Baker declined to do the regeneration (when he was dismissed from the role) for the following story, Time and the Rani.

In the serial, continuing from the events of Terror of the Vervoids, the genocide charges against the alien time traveller the Sixth Doctor for destroying the Vervoids are interrupted by the Doctor's enemy the Master (Anthony Ainley), who seeks to have the Doctor and his prosecutor the Valeyard (Michael Jayston) destroy one another in the virtual micro-universe the Matrix, and to create a power vacuum where the High Council of the Time Lords is deposed so the Master can take command.