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 but set the Cybermen on them but made the Cybermen capture 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 the cybermen,and herself in the process. (DW: The Next Doctor)
