The Duke of Forgill was a Scottish nobleman and the president of the Scottish Energy Commission. He was abducted by the Zygons and impersonated by their leader, Broton. The Fourth Doctor found the real Duke in the Zygon ship, along with the other abducted humans, and helped them escape prior to setting the ship to self-destruct.
He later accompanied the Doctor, the Brigadier, Harry Sullivan and Sarah Jane Smith to the Doctor's TARDIS. (TV: Terror of the Zygons)