Jask (The End of Time)

Commander Jask was a Sontaran commander who hunted Mickey Smith and Martha Jones. He was about to shoot the two from a platform, when the Tenth Doctor knocked him out by hitting his probic vent with a hammer. (TV: The End of Time)

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

The Big Finish audio The Sontaran Ordeal also had a Sontaran named Jask, also portrayed by Dan Starkey, although there is no other known evidence that they are the same character.