Torchwood is an organisation created by Queen Victoria in 1879 to study and protect the Earth against aliens (specifically the Doctor originally). They started collecting alien technology to use for themselves and to defend the planet. The Doctor was unaware of Torchwood until 2006 when he met Yvonne Hartman, the head of Torchwood 1 (one of the Torchwood bases). Later, when Torchwood 1 was destroyed, the Doctor discovered his friend Captain Jack Harkness also worked for Torchwood, though he worked for Torchwood 3 which was a very small group who did not necessarily want to kill and torture aliens. It is in quite a few ways like UNIT, though they do not own an army.
Out of Universe Edit
A spin-off show based on the Doctor Who universe following the Cardiff branch of the Torchwood Institute (Torchwood Three), led by Jack Harkness. The Institute was established at the end of "Tooth and Claw" and its nature first revealed in "Army of Ghosts" (which featured the London HQ, Torchwood One), before the series itself debuted in 2006. Four seasons of Torchwood aired sporadically between 2006 and 2011, with the third and fourth seasons formatted as a 5- and 10-part mini-series, respectively; the series is currently considered to be on indefinite hiatus with no word as to when or if a fifth season will be commissioned in the future.