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. 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 for the following story, Time and the Rani.

The twenty-third season of British science fiction television series Doctor Who, known collectively as The Trial of a Time Lord, aired in weekly episodes from 6 September to 6 December 1986. It contained four adventures: The Mysterious Planet, Mindwarp, Terror of the Vervoids and The Ultimate Foe; the season also marked the final regular appearance of Colin Baker as the Sixth Doctor.