The files constitute an unassigned project (outside the Bureau mainstream) that is more or less concerned with unexplained phenomena, fringe pseudo-scientific theories, and non-credible evidence of paranormal activity.
It contained information about a series of murders that occurred in the Northwestern U.S. during World War II, seven of which took place in Browning, Montana.
At first, he thought the X-Files seemed like "a garbage dump for UFO sightings, alien abduction reports; the kind of stuff that most people [would] laugh at as being ridiculous".
Blevins claimed to believe that Mulder had developed a consuming devotion to the X-Files and that Scully, who was trained as a medical doctor, would lend proper scientific analysis to the cases.
In the second season (1994–95), Mulder is operating as a general assignment agent when he receives an anonymous phone call from a mysterious man who tells him that the X-Files have to be reopened.
Once the two later met, the mysterious man claimed that the government conspiracy had killed "Deep Throat", closed down the X-Files and separated the agents assigned to the cases as an initial attempt to secure the truth they were hiding.
In the season two episode "Ascension", Mulder's superior, Assistant Director Walter Skinner, reopens the cases, aware that the X-Files are what the conspiracy fears most.
The X-Files Project was reinstated after Skinner contacted Scully, who was working in a private hospital, to get her and Mulder to meet Tad O'Malley, a conspiracy talk show host.
SCP Foundation - Similar albeit much larger and extragovernmental organisation dedicated to the research and containment of paranormal (anomalous) phenomena making up the namesake of the extremely large collaborative fiction universe it exists in.