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.

Melanie "Mel" Bush is a fictional character played by Bonnie Langford in the long-running British science fiction television series Doctor Who. A computer programmer from the 20th century who is a companion of the Sixth and Seventh Doctors, she was a regular in the programme from 1986 to 1987 and returned in 2022, 2023, and 2024. Mel appears in eight stories, and is the penultimate companion of the classic series.