Another impetus for finishing the arc was the belief of series creator and episode co-writer Chris Carter that the series would end by the spring of 2000. Thus "One Son" was written to resolve many of the show's arcs in preparation for a future series finale. The writing staff was also looking for ways to create a new story lines for the series, such as the "Super Soldiers" arc, which was created for the eighth and ninth seasons. Carter also sought to rectify small issues that fans had with the 1998 feature film, "The X-Files", explaining, "I think if there was any trouble with the movie, it was that we promised so much that we didn't deliver all of it. I think we wanted to deliver a lot, and all at once, in these two episodes". Episode co-writer Frank Spotnitz agreed, saying that when "The X-Files" film was being promoted with the tagline "The Truth is Revealed," he realized that many fans would be unhappy with the revelations. Spotnitz struggled when writing "One Son" because he believed that episodes that gave answers seemed to be less entertaining for viewers than episodes that presented new questions. He did, however, acknowledge that this episode was necessary to explain the show's mythology; he called the episode the "biggest chapter we had time to explore in the nine years we were on the air". Writers for the series often struggled with writing "mytharc" episodes because there was a need to force as much material into them as possible, given their relative paucity compared to the "Monster of the week" episodes. Originally, a large portion of the episode was supposed to reveal the history of the Syndicate via flashback. Reportedly, these scenes would have featured younger versions of Bill Mulder (played by Peter Donat), The Smoking Man, Dr. Openshaw, the Elders, and many others. However, this idea never panned out, and Carter and Spotnitz reframed the episode around narration, courtesy of the Smoking Man, whose scenes were completed under extreme pressure near the end of production. While the title of the previous episode, "Two Fathers", referred to both Bill Mulder and The Smoking Man, this episode was titled "One Son" to reflect the fact that Mulder was the only remaining son of either of these men, after the presumed death of Jeffrey Spender and the rejection of Alex Krycek. Several of the plot elements self-reference other episodes of the series. Fort Marlene's presence is a reference to the first season finale "The Erlenmeyer Flask," in which the alien fetus was first introduced; the term "purity control" is also a reference to this episode.