Staal

"I am General Staal of the Tenth Sontaran Battle Fleet, known as Staal the Undefeated."

- Staal

Staal or "Staal the Undefeated" was a Sontaran and General of the Tenth Sontaran Battle Fleet during the Sontaran Invasion of Earth.

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

Staal remained in the Sontaran flagship as he ordered his subordinateSkorr to attack UNIT. He was contacted by the Doctor shortly after claiming the 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)