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 officiate their relationship with a piece of paper

Biography
Sophie had romantic feelings for Craig, as he did for her, but they never did piece 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, much 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, proclaiming that he loved her. Sophie responded in kind, placing her hand on the console and kissing Craig, which resulted in the destruction of the ship. As the Doctor left, she and Craig saw him off. (DW: The Lodger)

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

She was broody when she went away for a weekend, leaving Alfie in his 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 and Alfie spoke his first word, "Doctor". (DW: Closing Time)