He and Sergeant Benton began as returning characters in the first place, having appeared with the Second Doctor in "The Web of Fear" and again in "The Invasion", prior to starting their full-time association with the Third and Fourth Doctors. Tegan Jovanka was the first full-time companion to part from the Doctor and subsequently return to full-time companionship, although the break in her tenure had been pre-planned. Most reappearances of companions in the original series, however, were for anniversary specials such as "The Five Doctors" and "Dimensions in Time", both of which also featured multiple Doctors. One former companion, Sarah Jane Smith, together with the robotic dog K-9, appeared in four and two episodes, respectively, of the revived series more than twenty years after their last appearances in the 20th anniversary story "The Five Doctors" (1983). The character of Sarah Jane also headed up a "Doctor Who" spin-off, "The Sarah Jane Adventures", with K-9 until Sladen's death. Another companion, Captain Jack Harkness, is the lead character in the spin-off BBC science fiction programme "Torchwood". Not only have these former companions continued to make appearances on "Doctor Who", they have sometimes been accompanied by some of their own companions from the spin-offs when doing so, including Jack's colleagues Gwen Cooper and Ianto Jones, and Sarah Jane's 'family' Mr Smith, Luke Smith and K-9 Mark IV. Other former companions from both the classic era and revived series have also returned as guest stars in the spin-offs, including Martha Jones on "Torchwood", and Brigadier Lethbridge-Stewart and Jo Grant on "The Sarah Jane Adventures". K-9 Mark I has also been spun off into its own series, albeit with an independent continuity. When "Doctor Who" returned to television in 2005, the companion characters played a slightly different role, partly due to a strong focus on the character of Rose Tyler and characters connected to her. For example, although Adam Mitchell was a companion by the standard definition, he appeared in only two episodes and was arguably a less significant part of the 2005 series than Rose's sometime boyfriend Mickey Smith, who was not technically a companion but appeared in five episodes (or six, including a brief appearance as a child in "Father's Day"). Mickey later gained full-fledged companion status when he travelled in the TARDIS in the 2006 episode "School Reunion". In that episode, Sarah Jane Smith referred to Rose as the Doctor's "assistant", a term to which the latter took offence.