Sophie (The Lodger)

Sophie was Craig Owens's girlfriend and the mother of their son, Alfie Owens, though the two were not married and didn't believe they needed to solemnise their relationship with a piece of paper

Biography
Sophie had romantic feelings for Craig, as he did for her, but they never pieced together that they loved each other. When Craig took in a new lodger, she found him very quirky and strange, but was inspired by him to follow her dream of helping animals, to Craig's chagrin. One day while the Doctor was at the flat, she was lured upstairs to an attempted time machine ship which was trying to kidnap a pilot. The Doctor and Craig saved her, with Craig, at the Doctor's insistence, placing his hand on the control panel. When asked by the Doctor why he didn't want to leave the flat, Craig replied that it was because he didn't want to leave Sophie, because he loved her. Sophie responded in kind, placing her hand on the console and kissing Craig, which destroyed the ship. As the Doctor left, Craig and she saw him off. (DW: The Lodger)

Some time after this, Craig and she moved in together. They had a son, Alfie. She was better at parenting than Craig. (DW: Up All Night)

Sophie was broody when she went away for a weekend, leaving Alfie in Craig's care. Unknown to her, the Doctor visited Craig that weekend and had an adventure with them. When she returned home she found the house completely cleaned up and Craig's relationship with their son vastly improved. Alfie spoke his first word, "Doctor". (DW: Closing Time)