Strax

Commander Strax was a Sontaran commander who was demoted to nurse by the Sontaran Empire. He fought and died at the Battle of Demon's Run, as a reimbursement to the Doctor as debt for saving his life.

Biography
Strax was one of many people who owed the Doctor a debt. (TV: A Good Man Goes to War)

In the year 4037, he was tending to human soldiers at the Battle of Zaruthstra when he was summoned by the Doctor to help in the mission to rescue Amy and her baby at Demon's Run, which offered him a chance to once again experience the pleasure of battle. He was mortally wounded in the battle with the Headless monks when one damaged his probic vent. In his final moments, Strax noted how he had once longed to die in combat (which was common among Sontarans), and now, he didn't find it as enjoyable as he had thought it would be. Rory tried to comfort him, saying he was sure he would recover, but Strax wasn't fooled, reminding Rory that he was a nurse, too. However, he admitted that he had had a good life, and was pleased to live nearly twelve years. (TV: A Good Man Goes to War)

A Sontaran named Strax later worked with Madame Vastra and Jenny Flint in the Victorian London. (TV: The Great Detective) It was unclear if this was the original Strax or one of the clones he had mentioned before. (TV: A Good Man Goes to War)

Personality
Strax generally displayed traits that were normal for a Sontaran, such as a willingness to die in battle and a love of fighting. Despite being demoted to nurse at some point in his life, Strax was still a fierce warrior who was willing to face overwhelming odds without hesitation or fear. An example of this trait was when he and several of the Doctor's allies were outnumbered by the Headless Monks yet fought valiantly against them. He also showed a willingness to kill people he had once helped; for example after healing a human boy he told him that he hoped to one day defeat him in mortal combat.

However, Strax also had a softer side and appeared to like children, tending to a young boy during the battle of Zaruthstra and offering to breastfeed Melody Pond, seeming rather affronted when Rory and Amy refused his offer. After becoming a nurse, he gene-spliced himself for all nursing duties. He told Rory that he could produce "magnificent quantities" of lactic fluid. Strax had vast medical knowledge, so much so that he would even give advice to his enemies during confrontation; as when the Doctor's forces surrounded Colonel Manton and his unarmed Clerics, Strax told him not to slump as it was bad for his spine.

Despite the fact that most Sontarans considered the Doctor to be an enemy, Strax was a loyal ally to the Time Lord and did not appear to have any grudge against him. At the end of his life, Strax commented that he wasn't enjoying dying in battle as much as he'd hoped. However he was grateful for having lived nearly twelve years which, for a Sontaran, was quite a long life. When Rory tried to comfort him, insisting that he was a warrior and he could survive, Strax reminded him that he was a nurse, apparently still holding resentment over his perceived demotion in his life. (TV: A Good Man Goes to War)

The Victorian era Strax "declared a war" on the Moon. He thought that it had been over them far too long and had gained a tactical advantage. When it was noted that the Moon was uninhabited, he stated that that meant "now is the best time to strike!" When something bad happened, thus, he was known to blame the moon, such as when the Eleventh Doctor "retired". (TV: The Great Detective)

Behind the Scenes

 * Strax is based on a disgraced Sontaran called Skrom from an unused Series 5 script by Gareth Roberts tenatively titled Death to the Doctor. Steven Moffat would later inform a delighted Roberts that his character idea would see the light of day. (REF: The Brilliant Book 2012)
 * According to The Brilliant Book 2012, a book that contains non-narrative based information; he met the Doctor on Earth in the past in an event which inspired the nursery-rhyme Humpty Dumpty, where Strax fell off a wall and was saved from death by the Eleventh Doctor.
 * Strax is the first recurring Sontaran in Doctor Who. However, the first recurring Sontaran character in the Doctor Who expanded universe was Commander Kaagh, who appeared in Series 2 of The Sarah Jane Adventures.