Kragar

Kragar was a Sontaran Psychic Surveyor within Psychic Command, under the orders of Commander Ritskaw, who considered him an old friend and comrade.

Biography
Kragar 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)

The initial Sontaran invasion of Earth exploiting the Flux event was repelled, (TV: War of the Sontarans) but after the Sontarans returned to occupy it with the Grand Serpent's help, Kragar oversaw Sontaran Psychic Command's experiments with boosting the native psychic talents of selected human prisoners to attempt to foresee the moment of the "final Flux event" coming to lash against the Lupari shield once again. After Claire Brown willingly gave herself up to the Sontarans as a means of infiltrating them, he succeeded in pinpointing the time of the Flux event, and was promised great honours.

The Sontaran fleet was later destroyed when Karvanista sabotaged their formation so that they would not be protected by the Lupari shield from the onslaught of the Flux. (TV: The Vanquishers)

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.