Kragar

Kragar was a Sontaran Psychic Surveyor under the orders of Commander Riskaw, who considered him an "old friend". He went on a long mission to investigate the Flux, during the course of which he became "withered" or, as Riskaw put it, much to Kragar's discomfort, "disgusting". After ascertaining that the Flux would cause "incredible suffering… vast bloodshed… a conflict that [would] dwarf all that [had] come before", Kragar sent Riskaw a holographic call on his ship to report this. This prompted an excited Riskaw to launch an attack. (TV: The Halloween Apocalypse)

Behind the scenes
Though best-known for the part of Strax, Dan Starkey, who played Kragar, had portrayed numerous other Sontarans in previous televised Doctor Who and The Sarah Jane Adventures stories, starting with Skorr and Skree in The Sontaran Stratagem/The Poison Sky. However, as Kragar, he was given notably different make-up than in his previous appearances as identical Sontarans.