Gwyneth (The Unquiet Dead)

Gwyneth was a servant girl at Gabriel Sneed's home in Cardiff who had clairvoyant abilities.

Profile
Her parents died of the flu when she was 12 and she was brought up by Mr. Sneed. She fancies the butchers boy

When Gwyneth gave the Doctor a cup of tea, she said, "Two sugar, sir. Just as you like it", although she had never met him before. These powers enabled her to be contacted by the gaseous Gelth who had arrived in the city via a space-time rift located there.

Gwyneth and the Doctor agreed to the Gelth's pleas to let them come through to Earth and possess dead bodies in order to survive. The Gelth lied to them about the extent of their numbers and their hostile intentions. When she stood underneath an archway in order to contact the Gelth, they passed through, and trapped the Doctor and Rose. To destroy them, she struck a match once the Doctor and Rose had escaped, igniting the gas in the chamber and destroying herself in the process.

Her actions appeared to be suicide until the Doctor told Rose that Gwyneth's body was already a corpse ever since stepping into the archway; even when she had told him that she would light the match. (DW: The Unquiet Dead)

Gwyneth's genetic traits would be passed, through the space-time rift via spatial genetic multiplicity, to her distant relative Gwen Cooper, an agent of the branch of the Torchwood Institute based in Cardiff in the 21st century. Gwen and Gwyneth looked practically identical, although Gwen did not inherit her psychic abilities. (DW: Journey's End).

Behind the Scenes
Though Eve Myles played both Gwen and Gwyneth, Russell T Davies denied in a Doctor Who Magazine interview that they were in any way related. However he reversed this position in Journey's End by having the Doctor and Rose Tyler comment on the resemblance and the Doctor explaining it and Gwen saying her family had lived in Cardiff for centuries.