Staal

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

He had a great love of warfare and regretted his race did not fight 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. (TV: 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 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. (TV: The Poison Sky)

Personality
Staal possessed a personality that was typical for a Sontaran. He loved warfare and was unafraid of death, even mocking the Doctor when the Time Lord threatened to blow up his ship. Staal was also manipulative and treacherous, having manipulated Luke Rattigan into helping him by saying that he would take him and some other teenagers to another planet to rebuild the human race, when he was actually planning to use him as target practice when he was no longer needed. Although he praised Private Harris's skills of deduction and called the Doctor a remarkable enemy, Staal showed no respect for humanity, claiming that "we say the same of humans" when Luke Rattigan asked how Sontarans told each other apart- which implied all humans looked the same to him. (TV: The Sontaran Stratagem)