Lisa Hallett

Lisa Hallett was an employee at Torchwood Tower in London at the time of the Battle of Canary Wharf. She was partially upgraded by the Cybermen and was hidden in the basement of Torchwood Three by Ianto Jones.

With Torchwood One
Like many other Torchwood staff, Lisa was taken to be upgraded into a Cyberman. However, the Cyber-conversion process was not completed, leaving her mostly human, but with numerous cybernetic implants. Her boyfriend and fellow Torchwood employee, Ianto Jones, helped her escape the ruins of Torchwood One and took her to Cardiff. (TW: Cyberwoman) He talked Jack Harkness into hiring him at Torchwood Three. (TW: Fragments) Taking advantage of Torchwood's cavernous Hub headquarters in Cardiff Bay, Jones found a remote room where he kept Lisa while he surreptitiously tried to restore her full humanity. (TW: Cyberwoman)

As a Cyberwoman
Dr. Tanizaki, a cybernetics expert, was brought in by Ianto to attempt to help remove the Cyber-implants. Unfortunately, his efforts instead caused the implants to become fully active, largely suppressing her original personality and causing her to embark on the Cybermen's mission to upgrade humanity. Hallett unwittingly killed Tanizaki while trying to Cyber-convert him, and then told Ianto that her desire was to become superior, just like the Cybermen. Ultimately, she escaped her chamber in the Hub and Jack and the others learned of her existence. She killed a Jubilee Pizza delivery girl and transplanted her brain into the girl's body in a last-ditch attempt at balancing humanity with Cyber-perfection. When it became clear that Lisa's original personality had been irreparably corrupted, she was killed by the other Torchwood Three personnel. (TW: Cyberwoman)

Post-mortem encounters
Lisa reappeared as a "spirit" who urged Ianto to open the Rift. This was merely an illusion projected to Ianto by Bilis Manger. (TW: End of Days) Later, Ianto had to endure another impersonation of Lisa during the incident at CERN in Switzerland. (BBCR: Lost Souls)

Abilities
Lisa was able to electrocute people with her hands and used a wrist-mounted blaster, much like a fully converted Cyberman. She was also stronger than a normal human being.

Behind the scenes

 * In Torchwood Magazine, it is suggested in an interview with Gareth David-Lloyd that Lisa is the reason Ianto Jones wears suits rather than the casual clothes he did the first time he met Jack. David-Lloyd states that Ianto wears his suits as a way of masking his true personality, and his intentions to find a cure for Lisa. However, once the death of Lisa comes about, David-Lloyd explains that Ianto becomes much more comfortable in both his suits, and his team.
 * Character Options released a Lisa Hallett figure as part of their line of Torchwood action figures.