(Season 4, Episode 17 / Often cited as S4E8 in specific contexts)
(Season 7, Episode 22 / Sometimes confused with S4) [S4E8] Requiem
Though it is the Season 7 finale, "Requiem" is one of the most famous episodes in the series, featuring the abduction of Fox Mulder. (Season 4, Episode 17 / Often cited as
: The X-Files Wikipedia overview notes how this episode transformed Special Agent Dana Scully from a skeptic into a "reluctant believer" after Mulder's disappearance. Other Shows with an Episode 8 Titled "Requiem" : For a broader look at the secrets
(Video Game): While not a TV episode, this recent release has generated significant discussion regarding its ending and the character Grace.
: For a broader look at the secrets revealed during this era of the show, the Raymond Reddington Wikipedia page summarizes the "imposter" theory and the role Kathryn played in hiding the truth.