Tenth Doctor Month: Meet The Companions - Captain Jack Harkness

Captain Jack Harkness was originally a Time Agent from the Boeshane Peninsula in the 51st Century, he awoke one morning to find that all his memories had been erased by his employers leaving him with no knowledge of what had happened to him during this period. On account of this Jack set himself up as a freelance conman, travelling to places such as first-century Pompeii and Second World War London, salvaging alien space junk and selling it back to the Time Agency before pre-known and natural causes resulted in their destruction. 

Basing himself in Westminster in 1941, Jack served as an American volunteer for the Royal Air Force; assuming the identity of the real Captain Jack Harkness. Having previously stolen a Chula vessel for himself, Jack conned the Ninth Doctor and Rose Tyler into believing the Chula hospital ship was actually a warship. A German bomb was scheduled to destroy it soon after. Jack prevented this bomb from falling on the crash site by suspending it in statison board his own ship but he was unable to jettison it. He was then rescued from his ship's destruction by the Doctor and Rose who invited him on board the TARDIS as their companion, even giving him his own key. (The Empty Child / The Doctor Dances)
He helped the Doctor and Rose to stop the Slitheen destroying Cardiff (Boom Town) and was then transported from the TARDIS to to the Game Station and a sinister recording of an alternative version of What Not To Wear. After a failed attempt to rescue Rose Tyer from The Weakest Link he was arrested alongside the Doctor and Lynda Moss and sentenced to imprisonment on Earth's Lunar Penal Colony. 

When they eventually escaped and uncovered an army of ships hidden from Game Station transmitters, Jack recognised them as Dalek ships, which he had seen during the Tenth Dalek Occupation. Jack served as the Doctor's last line of defence, ultimately being exterminated by the Daleks, although he was later resurrected by Rose, who used the power of the Time Vortex to bring him back to life, making him immortal in the process. The Doctor instinctively reacted against Jack's immortality and abandoned him on board the Game Station (Bad Wolf / The Parting Of The Ways).
Stranded in the year 200,100 Jack used his Vortex Manipulator to travel to Earth in 1869 but, when the Manipulator burnt out, was forced to live in the 20th Century, waiting for a version of the Doctor that coincided with his own timeline. 

Jack took the opportunity to visit his loyal friend Rose Tyler when she was growing up on the Powell Estate in the 1990s, though he would just watch her and not make contact with her. Knowing that the Doctor would have to return one day to refuel Jack based himself in Cardiff, on top of the rift that ran through the city.  Jack joined Torchwood in Cardiff and, following the Battle Of Canary Wharf, rebuilt it in the Doctor's honor to defend the Earth. He had retrieved the Doctor's severed hand after the Sycorax attack and kept it in order to detect the Time Lord's presence. He then travelled to the end of the Universe clinging on to the exterior of the TARDIS as it dematerialised from Cardiff in 2008 (Utopia), before helping the Tenth Doctor and Martha Jones defeat the Master upon their return to Earth. Though the Doctor asked him to come travelling in the TARDIS again, Jack returned to his team at Torchwood, but before the Doctor had disabled his Vortex Manipulator's travel abilities for a second time.
Charming and flirtatious to everyone he met Jack revealed that he had been the poster boy where he had grown up in the Boeshane Peninsula and was the first of his people ever to be signed up for the Time Agency. As a result, he told the Doctor and Martha that he had been nicknamed The Face Of Boe, leaving them to realise that their immortal friend would live to be their other old friend billions of years in to the future.
Although Jack said farewell to the Doctor and Martha at the end of Last Of The Time Lords it was not to be their final meeting.

In the alternative world where Donna Noble never met the Doctor, Jack was captured by Sontarans and transported to Sontar, leaving Gwen Cooper and Ianto Jones to destroy the Tenth Sontaran Battle Fleet, giving their lives in the process (Turn Left).
Jack, Gwen and Ianto were in the Torchwood Hub when Earth was moved to The Medusa Cascade the Daleks invaded Earth. Leaving his friends to deal with a Dalek, Jack took the Defabricator Gun and teleported to London in time to destroy the Dalek that shot the Doctor during his reunion with Rose. He, Rose and Donna watched in the TARDIS as the Doctor used regeneration energy to save himself and then they all travelled to the Medusa Cascade where the Daleks exterminated Jack. This was a ruse to allow Jack to infiltrate the Crucible, and he met up with Jackie Tyler, Mickey Smith and Sarah Jane Smith. Together they helped defeat Davros and the Daleks and when the returned to Earth Jack left with Martha Jones and Mickey.
Jack was in a bar on Zog when the Tenth Doctor came to say goodbye, but left him a note, telling him to introduce himself to the man sat next to him, Midshipman Alonso Frame, which Jack did...