Bill Potts

Bill Potts was a companion of the Twelfth Doctor. Her mother died when she was young, so she was brought up by a foster mother.

Later in life, Bill served chips at St Luke's University in Bristol, and attended the Doctor's lectures. Noticing this, he became her personal tutor. Another student, Heather, showed her a puddle that cast a reversed reflection. Bill asked Heather not to leave without her. As a result, when Heather was taken over by the puddle, she followed Bill home, so as not to leave without her.

Bill went to the Doctor, who brought her into the TARDIS. He tried to outrun the creature, and finally travelled to the Dalek-Movellan War. Bill realised she was being pursued as Heather had promised not to leave without her. On the Doctor's advice, she released Heather from her promise.

The Doctor took her back to the university, intending to wipe her memory of these events, but he was convinced not to. He then agreed to take Bill with him on his travels. (TV: The Pilot)