C is for... Cyber King

When a group of Cybus Cybermen escaped from the Void, using stolen Dalek technology, they found themselves stranded in Victorian London with little resources. They made contact with a woman named Miss Hartigan, who worked in a local poorhouse for the city's destitute children. She agreed to help them create the Cyber King. This was a gigantic machine shaped like a Cyberman but driven by steam power. Within was contained a full cyber-conversion factory. Children from a number of workhouses were used as slave labour to help with its construction. It required a controlling unit, and Miss Hartigan was shocked to discover that she was intended to become this. However, her strong will refused to allow her to be totally enslaved to the machine. She destroyed the Cyber Leader and took over, launching the machine on an attack on the city. The Doctor recognised it as a Dreadnought Class Cyberman craft.

The Cyber King had risen out of the Thames where it had been constructed and began firing on the city below. The Doctor took to a balloon to confront Miss Hartigan. He was able to show her that she had become a monster and the cyber-conditioning was broken. She perished - taking the Cybermen with her. The Doctor then used the Dalek device which had brought them here to open a portal into the Void. The collapsing Cyber King fell into this.
The Doctor was puzzled as to why this event was never later remembered. It transpired that the whole thing was deleted from history when the universe was rebooted by the Pandorica.

Played by: Dervla Kirwan (Miss Hartigan). Appearances: The Next Doctor (2008).