Oswin Oswald

Oswin Oswald was a human serving as a Junior Entertainment Manager onboard the starship Alaska when it crashed into the Dalek Asylum.

Oswald initially tried to escape the Asylum but was found and converted into a Dalek. Unlike other members of the Alaska, who were partially converted by the nanocloud, she was fully converted, due to her intelligence. In Dalek form she created a dream world for her human mind to dwell in to forget the truth. 

She aided the Eleventh Doctor, Amy and Rory in finding safe passage, wiping the memory of the Doctor from the Daleks' telepathic web in the process to save him. The Doctor attempted to rescue her, but discovered she was a Dalek and revealed it to her. Oswin first attempted to exterminate the Doctor, then broke down over what she had become.

_{Biography from the Tardis Wiki article, licensed under CC-BY-SA}