Rose Tyler (Billie Piper), a companion of the Ninth Doctor (Christopher Eccleston), meets him during the London Blitz. 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. Now working as a con man, Jack is responsible for unwittingly releasing a plague in London in 1941. 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. He subsequently travels with the Doctor and Rose in the Doctor's time-travelling spacecraft, the TARDIS. 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. 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. She and the Doctor subsequently leave Jack behind on Satellite 5. Jack returned in 2006 as a character of the spin-off series Torchwood, in which he is a member of the Cardiff-based Torchwood Three in combating alien threats and monitoring a spacetime rift which runs through Cardiff. Jack is re-introduced as a changed man, reluctantly immortal, having spent years on Earth waiting to reunite with the Doctor. Jack recruits policewoman Gwen Cooper (Eve Myles) to the team of experts after she discovers them; there are hints of romantic feelings between the two, but Gwen has a boyfriend and Jack enters a sexual relationship with the team's general factotum Ianto Jones (Gareth David-Lloyd). Despite having worked with him for some time, his present-day colleagues know very little about him; over the course of the series they discover that he cannot die. Jack was once a prisoner of war, and was an interrogator who used torture. In the Torchwood Series 1 finale "End of Days", Jack returns to the TARDIS. This immediately leads into the 2007 Doctor Who episode "Utopia", where he joins the Tenth Doctor (David Tennant) and his companion Martha Jones (Freema Agyeman). Jack explains he returned from Satellite 5 to the present day by travelling to 1869 via vortex manipulator, and lived through the 20th century waiting for the Doctor. By the series finale, having spent a year in an alternative timeline enslaved by The Master