Vastra
Vastra was a female Silurian warrior who shared a house with a human woman, Jenny in Victorian London. It is implied from dialogue between the two that they shared a both romantic and sexual relationship.
She was one of many people who owed the Doctor a debt: she awoke during the construction of part of the London Underground and wanted to take revenge on the workers for the deaths of her "sisters"; the Doctor convinced her not to give in to rage. Vastra would instead make a home in London, disguising her Silurian form to most people and acting as a freelance adventuress.
After eating Jack the Ripper, she was summoned by the Doctor to help in the mission to rescue Amy and her baby at Demon's Run. She and Jenny arrived at Demon's Run along with a army of Silurian soldiers, they both survived the battle with the Headless monks. It is implied she has known the Doctor for some time as she refers to him as an old friend. The Doctor also informed her on Time Lords as she refers to regeneration, the Untempered Schism and the time vortex . (DW: A Good Man Goes to War)
