A Good Man Goes to War
Strax is a member of the alien warrior race, the sontarans. Strax was forced to serve as a nurse, healing the injured as a punishment for being defeated by the Doctor during the Sontaran invasion of Earth. This is contrary to the Sontaran's warrior instincts and mentality and as such, Strax has been known to occasionally slip back to his Sontaran ways and mannerisms. In "A Good Man Goes to War", he states that he is nearly 12, suggesting that this is quite old for a Sontaran. Running jokes include Strax's inability to tell the difference between genders and his obsession with using violent tactics.