"William" is the sixteenth episode of the ninth season of the American science fiction television series The X-Files, which originally aired on the Fox network on April 28, 2002. The teleplay of the episode was written by series creator Chris Carter, from a story by former series star David Duchovny, Carter, and executive producer Frank Spotnitz; the entry was directed by Duchovny. "William" helps to explore the series' overarching mythology. The episode received a Nielsen household rating of 5.8, being watched by 6.1 million households and 9.3 million viewers upon its initial broadcast. It received mixed reviews from television critics, many of whom were unhappy with the episode's conclusion.

Frank Charles Spotnitz is an American television writer and producer. He is best known for his work on the series The X-Files (1995-2002) and its spin-off The Lone Gunmen (2001), and as the developer/creator of The Man in the High Castle (2015-19), Medici (2016-19), Ransom (2017-19), and Leonardo (2021-present)