Jask (The End of Time)

Commander Jask was a Sontaran who Mickey Smith and Martha Smith-Jones hunted. He was about to shoot them when the Doctor knocked him out with a hammer to his probic vent.

Behind the Scenes
Jask was not named on screen or in the credits. However, his name is given in the script to The End of Time Part 2, which is avalaible for download on the website for The Writer's Tale.

Jask bears an uncanny resemblance to Commander Skorr, who was also played by Dan Starkey. Considering the clone nature of Sontarans some resemblance is to be expected