<P> The character was originally created purely for the plot of "Silence in the Library". Moffat knew that the team of archaeologists would have to trust the Doctor, but the Doctor's psychic paper could not explain and convince the team why he had appeared in a sealed - off library . Therefore, Moffat intended for the Doctor to know one of the archaeologists, but decided that idea was "dull" and instead decided to have one of them know him . When Kingston returned to the show, Moffat explained to her some details about her character's back - story, knowledge which Smith, Gillan and Darvill did not receive until later . Kingston relates that she knows her character cannot be killed off because we saw her death in her introductory episode; each subsequent appearance is set at a different point in her character's personal history . Moffat had planned out that River was Amy and Rory's daughter for "a long time" and used "Pond" as Amy's last name to create a link between the two . For the filming of the sixth series, Kingston was aware of River Song's relationship to Amy and Rory, while the other cast only found out upon reading of the mid-season cliffhanger script for "A Good Man Goes to War". </P> <P> Moffat was influenced by Audrey Niffenegger's science fiction romance novel The Time Traveler's Wife, which depicts a woman who romances and marries a man who unintentionally moves through time . Niffenegger's lovers experience an asynchronous and tragic love story . He comments, "I've quite purposefully used it", though he cites his 2006 episode "The Girl in the Fireplace" as the episode which most prominently explores the book's themes in addition to its conceit . Kingston herself compares the character to Niffenegger's titular Time Traveler's Wife, and like Moffat enjoys "backtracking" more and more with the character as the series progresses . The tragedy for Song highlighted by "The Impossible Astronaut" / "Day of the Moon" is that she is progressing to a point where the Doctor will not know or trust her any more . Kingston comments, </P> <P> (What) Steven explained to me is that every time River sort of finds the Doctor, for whatever reason, she's never 100 percent sure which Doctor it is she's going to be meeting . And what they have already experienced together or not . So even when I come back, every time I meet Matt, I never quite know where we are in our relationship or what we have revealed or what we know about each other . Because time travel isn't linear . </P> <P> Kingston describes the character as being "like a female Indiana Jones" with regard to both characters being archaeologists and having action hero qualities . She also took inspiration from Sigourney Weaver's portrayal of Ellen Ripley in the Alien film franchise commenting that she'd always been "so envious of her for having that kind of role ." Kingston has also praised the way the love story between River and the Doctor has been deftly handled, stating that "I'm not sure you'd get that kind of dynamic in America". For Kingston, the physical age difference between herself and Matt Smith adds to the success of the pairing, whilst she feels that viewers have responded warmly to the notion of an action hero in her 40s . Matt Smith has noted that in his characterisation of the Doctor that "River Song frightens the Doctor but he finds himself strangely attracted to her" and that "what makes her a great companion is that when she turns up all hell breaks loose!". </P>

When does river song first meet the doctor