Ruth Mills

In a parallel universe, Ruth Mills was a human whose father, Eric Vollmer, died in the Deep-sea Energy Exploration Project base in 2039. The Doctor promised he would take care of his daughter. The death of Eric Vollmer came with the destruction of fish stocks around the base, making people lose their livelihoods. Ruth and her mother changed their name from Vollmer to Mills to stop others from ruining their lives. Ruth discovered 27 years later that it was the Doctor who killed Vollmer to cover up the genetic super-soldier experiments taking place at the base. She also learnt that because she knew too much about what happened, she herself was expendable. She shot the Doctor, making him regenerate into a new incarnation, then planned to keep shooting him until he remained dead. (AUDIO: Full Fathom Five)