Reggie Murgatroyd or Reggie "Something" (played by Brian Huskey) was a mentally unstable man, who claimed that he was a FBI partner of Mulder and Scully earlier and created the X-Files, but because of Dr. They and the Mandela (or Mengele) effect, they forgot this. Reggie was involved in the occupation of Grenada and worked for various public offices (CIA, NSA). He was later transported to the Spotnitz sanatorium. (TXF: "The Lost Art of Forehead Sweat"). Reggie was known by Skinner and seems to really have worked with the FBI (maybe in a parallel universe). (TXF: "This", "The Lost Art of Forehead Sweat").
Interestingly, Mulder did indeed call a "Reggie" (Reggie Purdue), but he was murdered by John Barnett in 1993.(TXF: "Young at Heart").