Walter Sergei Skinner is a fictional character played by Mitch Pileggi on the 1993-2002 television series the X-Files. Skinner is an Assistant Director in the FBI and is the direct supervisor of Special Agents Mulder and Scully.

Initially, A.D. Skinner is not disposed to trust Agent Mulder and his research of the paranormal, although it is unclear whether he is entirely independent in his actions or is controlled by people such as the Cigarette Smoking Man. The frequent presence of Cigarette Smoking Man in Skinner's office suggests that Skinner was at least partially controlled, however. Eventually, Skinner starts trusting Mulder and Scully and becomes their ally.

Walter Skinner is a former Marine and a Vietnam War veteran. He was married to Sharon Skinner, from whom he was divorced on March 7, 1996 after 17 years of marriage. He has been treated at a sleep disorder clinic, suffering from recurring dreams of an old woman, which may be a consequence of drug use during Vietnam or may be a succubus. Skinner's hobbies include jogging and boxing.