Kragar

Kragar was a Sontaran Psychic Surveyor within Psychic Command, under the orders of Commander Ritskaw, who considered him an old friend and comrade. He went on a long mission to investigate the Flux, during the course of which he became "withered", or as Ritskaw put it—much to Kragar's discomfort—"disgusting". Kragar sent Ritskaw a holographic call on his ship to report that after ascertaining the Flux would cause "incredible suffering, vast bloodshed, a conflict that would dwarf all that had come before", giving the Sontarans the perfect opportunity to take advantage of the catastrophe. This prompted an excited Ritskaw to launch their attack. (TV: The Halloween Apocalypse)

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