The Valeyard was played by Michael Jayston who we were lucky enough to meet at Bedford Who convention, and what a great person he is!  Very witty, intelligent and kind, and happy to slip out for a cigarette with Darren at every opportunity! The Valeyard was described by the Master as an amalgamation of the Doctor's darker sides from between his twelfth and final incarnations. In the story The Trial of a Time Lord, comprising the whole of Season 23, the High Council of the Time Lords appoint the Valeyard as prosecutor at the Sixth Doctor's trial, hoping to have him executed and thereby remove the sole witness to their near destruction of life on Earth.