Captain Jack Harkness is the lead character in Torchwood, a spinoff series from the Doctor Who universe, a hallmark of UK television. He first appeared in "The Empty Child," a Doctor Who episode broadcast on 21 May 2005. From that point, he appeared in all the episodes of the show until the first season finale.
The TV series Torchwood, which airs on the BBC Three network, was then introduced on December 2006. Jack Harness also appeared in three episodes of the third season of Doctor Who (2007) and is one of the rare television characters who finds himself being developed through dual series.
Jack Harkness, or Captain Jack, is a time traveling con man from the 51st century. He is bisexual, even pansexual, it is sometimes said, explaining that in the 51st century, with man's discovery that he is not alone in the world, sexuality has become a lot more unimportant.
Not much is known of Jack Harkness's youth. In fact, we don't even his real name. His current identity is one he stole from a dead World War II soldier, whom he subsequently met and fell in love with in an episode of Torchwood which involved a temporal rift. It is known, however, that he is from the Boeshane Peninsula, and was the first man from that region to join the Time Agency, earning him the nickname of "Face of Boe." Incidentally, the "Face of Boe" is also the name of the oldest being in the universe, a creature whose whole body is shaped like a giant face, and whom the Doctor has encountered on several occasions, one of them being its death. We are led to conclude that Jack Harkness and the Face of Boe are one and the same, his unprecedented life span being a result of an occurrence in the season 1 finale of Doctor Who.
At present, Captain Jack is a member of Torchwood, an agency originated by Queen Victoria to conduct research on extraterrestrials on Earth. He leads Torchwood Three, a branch of the agency which happens to be located on a space time rift and is first mentioned in the Doctor Who episode "The Unquiet Dead," in Cardiff, Wales. The headquarters, also called the Hub, is underground and is filled with all sorts of alien technology.
Captain Jack supervises a team which includes a police officer (Gwen Cooper), a doctor (Dr. Owen Harper), a computer specialist (Toshiko Sato), and a general support man who seems to take on the roles of an all-around butler (Ianto Jones). While Jack Harkness is the indisputable leader of his team, he gladly takes a backseat when with the Doctor, obeying orders almost without question. He is portrayed as a strong leader (Torchwood) and a dependable second-in-command (Doctor Who) with a good grasp of technology - terrestrial and otherwise. Much like the doctor, he is seen confronting morally ambiguous situations heads on.
In terms of romance, Jack Harkness is implied to be having an affair with Ianto Jones, one of his employees. He is also hinted to have feelings for the Doctor, although he has never acted on them as the Doctor seems to be portrayed as a creature a little above ordinary romantic interactions.