

She and the Doctor subsequently leave Jack behind on Satellite 5. Rose brings him back to life while suffused with the power of the time vortex, but when the power leaves her she doesn't remember doing it.

During his time with the Doctor, Jack matures into a hero, and in his final 2005 appearance, he sacrifices himself fighting the evil alien Daleks. He subsequently travels with the Doctor and Rose in the Doctor's time traveling spacecraft, the TARDIS. After the Doctor cures the plague, Jack redeems himself by taking an unexploded bomb into his ship the Doctor and Rose rescue him moments before it explodes.

Now working as a con man, Jack is responsible for unwittingly releasing a plague in London in 1941. Although posing as an American volunteering in the Royal Air Force, Jack is actually a former 'Time Agent' from the 51st century who left the agency after inexplicably losing two years of his memory.

Jack Harkness first appeared in the 2005 Doctor Who episode 'The Empty Child' and its continuation 'The Doctor Dances', when Rose (Billie Piper), a companion of the Ninth Doctor (Christopher Eccleston), meets him during the Blitz. Aspects of the character's backstory-both prior to meeting the Doctor, and during his many decades living on Earth-are gradually revealed over Torchwood (and to a lesser extent, Doctor Who) through the use of flashback scenes and expository dialogue. Eventually, he reunites with the Tenth Doctor (David Tennant) for several appearances in Doctor Who. He spends over a century waiting to reunite with the Doctor, over which time he becomes Torchwood's leader. There he becomes a member of Torchwood, a British organization dedicated to combating alien threats. As a consequence of his death and resurrection in the 2005 Doctor Who finale, Jack becomes immortal and is stranded on 19th-century Earth. In the programme's narrative, Jack begins as a time traveller and former con man from the 51st century, who comes to travel with the Ninth Doctor (Christopher Eccleston) and his companion Rose (Billie Piper). In contrast to the Doctor, Jack is more of a conventional action hero, as well as outwardly flirtatious and capable of acts which the Doctor would view as less than noble.
