Volos

 told Tegan Jovanka and Vislor Turlough about their experiments and what their species did. He was worried about Konis' changes to the engine. He worked out a way to enter the world without being harmed and Tegan took advantage of this. He didn't realise that Konis had forseen this an set a trap and to all intense and purposes killed Tegan. He learnt that the facility he used hadn't been upgraded in years and that's why Tegan became frozen. He was put in charge of restoring the TARDIS console. He was a war orphan. His mind was the one who created the Vodyani. (AUDIO: Nightmare Country)