Jane Doe was an insane serial killer who operated in Gotham City under the employment of the Wrath, the "Anti-Batman". Doe would find her victims and use skin graffs to impersonate them for a while, taking over their lives before she killed them and began to wear their skins. It was this skill of Doe's that brought her under the Wrath's wing.
An expert mimic with no skin, only her muscle being visible, Jane Doe operated without an identity. She found a victim and assumed their identity, once fully immersed in the victim's life, Doe killed them and wore their skin. Once the skin had gotten worn she discarded it to look for a new victim. Her crimes brought her into the sights of the Batman relatively quickly, though she was rescued by the madman known as the Wrath, whose obsession with hunting officers in the GCPD brought him to give Doe an offer.
Infiltrating the GCPD for the Wrath, Doe assumed the life of Harvey Bullock. She kidnapped Bullock and got involved in his life, even getting him a girlfriend, GCPD Psych Profiler Abigail Wilbur. However, as Bullock her interest in cases related to the Wrath led to the Batman pointing her out. After being defeated and sent off to incarceration, like many before her, Doe vowed to escape and kill the Dark Knight.