Sergei Akunin

 was a member of the HMS Aquitaine who met with Nyssa after she was separated from the Fifth Doctor and Tegan Jovanka. He tried to help Nyssa when he was infected. After another time storm he encountered the Doctor. He had created the Akunite as a way to save a plant species and his colleagues. He was infected by Freya Jennings as revenge. The Doctor rescued him from the black hole before he could create the Akunite. (AUDIO: Aquitaine)