Strax

Commander Strax was a Sontaran commander who was demoted to nurse as punishment for an unspecified failure. He was one of many people who owed the Doctor a debt. In the year 4037, he was tending to near-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. 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, and now, he didn't find it as enjoyable as he thought. 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, stating that he reached 12 years old.

For a Sontaran, Strax was very emotional and had an amiable relationship with the others in the Doctor's rescue party. He showed an affection for children, saying to one boy he healed that he should become a great warrior and also offering to nurse Amy's baby - he gene-spliced himself to produce "magnificent quantities of lactic fluid."(DW: A Good Man Goes to War)