With the Inquisitor (Lynda Bellingham) overseeing the proceedings, it was the Valeyard (Michael Jayston) who proved the greatest threat, hiding his own sinister motives for wanting the Doctor's downfall.
Doctor Who: The Collection – Season 23 (The Trial of a Time Lord) includes the following stories from 1986:
The Mysterious Planet
Mindwarp
Terror of the Vervoids
The Ultimate Foe
Joining Baker[...]
Valeyard Archives
I've been to Gallifrey One a couple times even.
I've enjoyed all the talk about the 50th anniversary, and all the theories on the message board since the mention of The Valeyard at the end of The Name Of The Doctor. The Valeyard was first seen in The Trial Of A Timelord, in the Colin Baker 6th Doctor era, and[...]