Mercy Hartigan

Mercy Hartigan also known as Miss Hartigan was a human agent of the Cybermen, she assisted them in their attempt to conquer Victorian Britain and ultimately the world.

She was in charge of a sick house but when she met the Cybermen she ended up working for them coming up with unrational ways to serve and assist them. She went to a funeral of a vicar who had donated money to help children in workhouses setting Cybermen on the mourners but capturing the owners of the workhouses.

They led children to a factory by the docks and made them work the mechanics so that the CyberKing would rise. She killed the workhouse owners and the Cyber-Leader decided to convert her into the CyberKing. The Doctor then used a device made from Infostamps to break the link between her and the Cybermen. She then saw what she had become and destroyed both the Cybermen and herself in the process. (DW: The Next Doctor)

her personal character is that of a woman so twisted by hate and rage she has become merciless compasionless, but also extremely driven and resentfull of her second class status as a woman in a Victorian era. the extent of her negative emotions and drive is so great even cyber-conditioning failed and her mind was able to take control of the cybermen, once attached to the cyberking. it can be implied from dialog that she may have been raped and/or a prostitute earlier in life (though this is fan speculation) which would explain her negative emotions and specific hatred for men.