Konis

 was the Master engineer. The Fifth Doctor allowed them to use part of the TARDIS for one of their experiments. It was building them a world of their own. He had made changes to the engines design but didn't tell his people the truth of them, and hid shortly after this. Vislor Turlough managed to fish him out and he explained that outdated code caused Tegan to freeze. He wanted to create a fully fledged world. He worked out that Volos was the reason the Vodyani existed. (AUDIO: Nightmare Country)