Technician Ruvis was a Valethske.
Ruvis was part of the scientific team aboard the Valethske ship on the Great Mission. He was once a hunter but developed cancer after subsisting on Sontaran flesh for "three Lunar cycles". He was fitted with mechanical substitutes for the parts of his body destroyed by the disease, including his jaw and one of his legs. He was given the choice of ending his life honourably in a suicide mission, but chose instead to become a scientist, something Kikker thought was a "coward's way out".
He tried to use Peri in a breeding experiment to create domesticated humans.