Ritskaw

Ritskaw was a Sontaran Commander. He was an "old friend" of Psychic Surveyor Kragar.

Biography
After finishing his investigation of the Flux, Kragar called Ritskaw on his ship. Ritskaw was excited by the news of a greater cataclysm than had ever been known, deciding to use the opportunity to strike other species while they were at their weakest; he soon ordered an attack just as Earth was bearing the brunt of the Flux cloud. (TV: The Halloween Apocalypse)

Behind the Scenes
In the credits for The Halloween Apocalypse, this character's name was spelled as "Ritskaw". In the following episode, War of the Sontarans, in which the character features more prominently, he is in the credits and on the BBC iPlayer subtitles at the 52 minute mark as "Riskaw".