FBI Assistant Director Walter Sergei Skinner is a fictional character portrayed by American actor Mitch Pileggi on The X-Files and its short-lived spin-off The Lone Gunmen, both broadcast on Fox.

In the science fiction-supernatural series, Skinner supervised the X-Files office, which is concerned with unresolved FBI cases of mysterious or possibly supernatural circumstances.

He has been treated at a sleep disorder clinic, suffering from recurring dreams of an old woman, which may either be a hallucination arising from drug use during Vietnam or a succubus.

[2] Skinner's hobbies include jogging and boxing, the latter of which has been shown in his ability to outfight Fox Mulder and X and to defend himself reasonably well when he was attacked by Alex Krycek and his men.

[9] The role of Walter Skinner was played by actor Mitch Pileggi, who had unsuccessfully auditioned for two or three other characters on The X-Files before getting the part.

When the actor had attended the audition for Walter Skinner, he had been in a grumpy mood and had allowed his small amount of hair to grow back.

[11] Pileggi himself thought he got the role because of Gillian Anderson's (who portrayed Dana Scully) pregnancy during the second season, saying the producers felt they needed to take the "show in a different direction" while she was pregnant.

[10] In an interview with X-Files fan site host Robin Mayhall, Pileggi commented once that he felt David Duchovny's (portrayed Fox Mulder) semi-departure in season eight and the introduction of Robert Patrick's John Doggett, and the fact that he started to believe in Aliens at the end of season seven, Skinner was given the "opportunity to grow", further stating "new avenues" had been opened.

He was included in the film's plot only when a fitting opportunity to involve him arose, and Spotnitz and Carter were very happy to write Skinner into the story.

[19] George Avalos and Michael Liedtke from the Contra Costa Times both reacted positively to the death of Alex Krycek at the hands of Skinner, saying it was the best scene of the eighth-season finale, "Existence".