Captain Jack Harkness, portrayed by John Barrowman, first appeared in Doctor Who in the 2005 episode “The Empty Child” and is in the show throughout the rest of the 2005 series as a companion of the Ninth Doctor.
Jack later becomes the main character in Torchwood, an adult-themed spin-off of Doctor Who. He comes back into Doctor Who in the 2007 series and he meets the Tenth Doctor, and returned again for the 2008 series.
Jack is a time traveler and former con man from the 51st century. A bisexual. In contrast to the wiser and older Doctor, Jack prefers a hands-on solution to the problem at hand. As a consequence of his death and being brought back in the last episode of the 2005 series of Doctor Who, the character becomes immortal, which does not change during both Doctor Who and Torchwood.