Lynda Moss was one of the far future Big Brother contestants onboard the Game Station.
When she met the Doctor, he said that she was very sweet and asked her to join him on his travels. Lynda agreed and they set out to save Rose Tyler from her "death" during The Weakest Link. (DW: Bad Wolf)
Soon afterwards, Lynda met Captain Jack Harkness and helped them all battle against the massive Dalek invasion. She lost her life when a Dalek destroyed the observation deck, blowing Lynda into the vacuum of space. (DW: The Parting of the Ways) However this is skeptical as Rose could have brought her back to life as she had done with Jack.
Lynda was seen as one of the people who died for the Doctor. (DW: Journey's End)
Personality
Lynda was a very bright, bubbly, cheerful person. She became fast friends with The Doctor, which is why he asked her to accompany him. She seemed very concerned about what people thought of her, incessantly asking the Doctor if viewers of Big Brother on Earth liked her, to which he absentmindedly responded that people thought she was sweet.
She showed strong loyalty towards and great trust in The Doctor, despite only having known him for a few hours, as she stuck by his side assisting him even when she was told to get to safety. She had faith that he would keep her safe and fulfill his promise to her by taking her on the TARDIS with him. Just before she died and the hands of the Daleks, Lynda screamed as she realised her fate, and the Doctor was distraught at having failed her.
Lynda continued to haunt the Doctor's memories, along with other people who have died because of him.
Notes
- Occasionally Lynda is considered a companion of the Doctor by fans due to (similarly to Astrid) her accepting the Doctor's offer to travel in the TARDIS before dying prevented her from joining him. More accurately, Lynda could be considered the first "would-be companion", (a term that could also be applied to Jeanne-Antoinette Poisson, Astrid, Bayldon Copper, Jenny, and Christina de Souza) in that she wished to travel with the Doctor, but never got the chance.