"Torchwood" is an anagram of "Doctor Who". When the first series of Doctor Who (2005) was being made, television pirates were desperate to acquire the preview tapes. One of the people in the office had the idea of labeling the tapes with the anagram "Torchwood" rather than "Doctor Who", as a security measure to disguise the tapes when they were delivered from Cardiff to London. Writer Russell T. Davies liked this idea so much that it later inspired him to use it as a title when creating this spin-off series.
In certain episodes, Torchwood members use a drug called "Retcon" to wipe the memories of people who know too much about the organization. Retcon is a term derived from "Retroactive Continuity" and is used in serialized fiction, especially comic books, for when new events effectively change or erase the established history of a series.
Owen and Suzie are the only members of the Torchwood team never to have had direct contact with the Doctor. Jack has been companion to both the Ninth, Tenth and thirteenth incarnations; Toshiko met the Ninth Doctor while examining the space pig in Aliens of London (2005); and Gwen and Ianto met the Tenth Doctor through the sub-wave network in The Stolen Earth (2008).
Torchwood was the subject of a background arc during the 2006 series of Doctor Who, with most episodes containing at least one reference to the Torchwood Institute, beginning with Bad Wolf (2005) and culminating in the Institute's appearance in Army of Ghosts (2006) and Doomsday (2006). Tooth and Claw (2006) details the origins of Torchwood. After the "Torchwood" spin-off's debut, it was referenced again in The Runaway Bride (2006).
In several episodes throughout series 1, posters bearing the slogan "Vote Saxon" are visible in several shots, most noticeable in Captain Jack Harkness (2007) on the door of the dance hall. In series 3 of Doctor Who (2005), which was broadcasting during the same year, "Saxon" was the running keyword arc and the identity of "Mr Saxon" was the subject of the season finale.