General Mariah Learman was ruler of New Britain. She ruled some time in the mid 2010s. She was obsessed with William Shakespeare and researched time travel methods in an effort to preserve Shakespeare's work.
She was also part of a time loop involving the Daleks.
At an unspecified time, at a crucial point in her time travel experiments, a Dalek escape time corridor locked onto her time travel experiment, which utilised Orthopositronium, bringing the Daleks to the palace. She attempted contact with one of the Daleks, the pilot, destroying it.
Through a series of events, the Daleks made a working time travel machine out of Learman's equipment. However they required a pilot for their ship with the requisite time travel knowledge.
Learman was chosen to replace the Dalek that had been destroyed. She was given drugs and forced through an irradiated area filled with radiation, force-growing her into a Dalek mutant. The Learman Dalek was sent back to the Daleks' ship and she became the Dalek she encountered in her past. (BFA: The Time of the Daleks)