History of Doctor Who the UK in the spring of 2007 and began airing in Canada and the US during the summer of that year. A 2007 Christmas Special "Voyage of the Damned" was broadcast on 25 December 2007 in the UK, featuring Kylie Minogue as a waitress named Astrid. The fourth series aired in the UK in 2008 featuring two companions; Donna Noble, who first appeared in "The Runaway Bride" and Martha Jones, who returned to the series for five episodes of series four. Billie Piper also returned to the show to reprise her original role as Rose Tyler. Following broadcast of the
Companion (Doctor Who) in the Series Four finale "The Stolen Earth" / "Journey's End" (2008), which features a record eight past, present and future companions: Donna is joined by a returning Rose, Martha, Jack, Sarah Jane, and Mickey, while past companion K9 and future companion Wilfred Mott make appearances. This tendency, plus the increase in "one-off" companions like Astrid Peth and Jackson Lake, has further obscured the matter of who is and is not a companion. The Doctor's companions have assumed a variety of roles—involuntary passengers, assistants (particularly Liz Shaw), friends, and fellow adventurers; and, of course, he regularly gains new companions and