David Duchovny
The story for "William" was written by former series co-star David Duchovny, series creator Chris Carter, and executive producer Frank Spotnitz; the screenplay was written solely by Carter, and the entry was directed by Duchovny. "William" marked the return of David Duchovny, in some capacity, to the series, after his departure following the eighth season finale "Existence". In fact, Duchovny makes a cameo appearance in the episode, appearing as a reflection in Scully's eye.