Dethras

 was a Xancari scientist. He was part of a British submarine crew called John. The Fourth Doctor realised that he wasn't part of the crew by the fact that he knew it was primitive and was scared when he appeared. He discovered the theory of hyper-evolution and experimented on the humans which Flague had taken. He realised that research was wrong and destroyed it and took his experiments away for them to live in peace and not be used. The Doctor told him that this was futile as if Flague ever captured one of his creatures. When the Doctor took the creatures to a primitive world he stayed behind to help them become human again. (AUDIO: Dethras)