Staal

General Staal "The Undefeated" of the Tenth Sontaran Battle Fleet was a Sontaran General during the Sontaran Infiltration of Earth.

Biography
He had a great love of warfare and regretted that his race were not involved in the Last Great Time War, which he considered the universe's greatest war. He forged an alliance with Luke Rattigan to aid the Sontaran conquest of Earth. He had an ambition to personally kill the Tenth Doctor on meeting him. (DW: The Sontaran Stratagem)

Staal remained in the Sontaran flagship when he ordered his subordinate Skorr to attack UNIT. He was contacted by the Doctor shortly after claiming the Doctor's TARDIS as his trophy. After his plan of turning Earth into a cloning planet for more troops failed, he furiously decided to destroy Earth by force.

Rejecting the Doctor's offer to let him leave Earth alone or else be incinerated, Staal mocked him. He and all but one of his troops were then killed by Luke, who gave his life to destroy the flagship. (DW: The Poison Sky)