A 20-year-old blond skinny youth, whom the Doctor first meets on a planet, on which he has lived as long as he can remember. He is blunt, occasionally aggressive, but has an engaging personality. Despite his bluntness, he's chirpy and ever-ready with an amusing quip. We will eventually discover he is in the employ (or under the control) of the Black Guardian.
Turlough wishes to join forces with the Doctor in order to gain access to the TARDIS. In Turlough's first story, during which the Doctor will save his life, we will be sure that the youth is worthy of joining the Doctor - this will be achieved at the end of the four parter, though Nyssa and Tegan will be suspicious of the boy's motives and surprised at the Doctor's blindness to Turlough's deviousness.
In the second story, Turlough will attempt to engineer the downfall of the Doctor. The Doctor and companions will not realize Turlough's involvement, though the audience, of course, will. Needless to say the plan fails, and we end this story with the Doctor's suspicions aroused as to Turlough's credibility.
In Turlough's third story, the Doctor will have his suspicions confirmed and once again foils the boy's schemes, and dispense with the Black Guardian.
Turlough may or may not continue with the Doctor, but whichever is decided, Turlough will turn over a new leaf (perhaps!).
BBC Character Outline.
John Nathan-Torner. 15 May 1981.