On the television series The X-Files, an X-File is a fictional case that has been deemed unsolvable by the Federal Bureau of Investigation. (TXF: "Dæmonicus") The files constitute an unassigned project outside the Bureau mainstream that is more or less concerned with unexplained phenomena. (TXF: "Pilot")

According to the series mythology the very first X-File was initiated in 1946 by J. Edgar Hoover. It contained information about a series of murders that occurred in Northwest America during World War II, seven of which took place in Browning, Montana. Each of the victims were basically ripped to shreds and consumed, as if by a wild animal. However, many of the victims were found in their homes, as if they had allowed the killer to enter. In 1946, police cornered what they believed to be such an animal in a cabin in Glacier National Park. They shot it, but when they entered the cabin to retrieve the carcass, they found only the body of Richard Watkins. The murders stopped that year. Believing that the case was too bizarre to be solved adequately, Hoover labeled it unsolved and locked it away in the hope that it would eventually be forgotten. However, the murders resumed in 1954 and continued to occur every few years.