From the begining... 1980 - 1989 (10)

May 1980
Fox Mulder graduates from High School. (Based on being 18 year old at graduation.)

1982
FBI agent Duane Barry is shot in the head. He survives, but has severe mental problems for the rest of his life. He later believes that he is repeatedly abducted by aliens. His wife and family leave him. (Duane Barry)

Sergeant John Doggett, USMC, begins service with the Multi-national peacekeeping force in Lebanon. (Within)

Fall 1982
Dana Scully enters college, receiving an undergraduate degree in physics from the University of Maryland, taking courses in German (Unruhe) and Greek (Hollywood A.D.) and writing a "senior thesis" on Einstein's Twins Paradox. (Pilot) (An X-Files novel suggests she spends her first year at the University of California, Berkley and then transfers to Maryland.)

1983
Eve 6 is incarcerated in the Whiting Institute for the Criminally Insane, according to what she told Mulder and Scully in 1993. She claims to be the continuing subject of tests under the Litchfield Experiment. (Eve)

Fox Mulder enters college, graduating from Oxford with a degree in psychology in 1986. (Date from resume screen in Unusual Suspects.)
While at Oxford, he develops a relationship with Phoebe Green, who herself becomes a British law enforcement officer. He later comments that it took him ten years to forget about her, which would place it at about the time he will meet Scully. Fox and Phoebe share a "certain youthful indiscretion" atop the tomb of A. Conan Doyle. (Fire)

1986
Fox Mulder completes his Oxford degree in Psychology. In the Pilot, Mulder tells Scully "I went off to school in England, I came back, got recruited by the Bureau..." implying his entire college career may have been in England. (From resume seen in Unusual Suspects.)

Mulder is given the FBI badge number 22791. (The Amazing Maleeni)

Sometime in 1986 Gibson Praise is born. He later indicates that he lives in the Philipeenes, but details are unclear. (Might he be a US military dependent or son of an American business person?) Mulder later finds evidence suggesting that Gibson has alien DNA, allowing him to read minds. (The End)

Mulder graduates at the top of his 15-week class at the Quantico FBI academy, earning the nickname "Spooky." (From resume seen in Unusual Suspects.)

In many ways he is a protege of William Patterson. Famous in the FBI for his skill as a criminologist, Patterson teaches that it is necessary to "become the monster" in order to understand the murdered. Mulder feels Patterson dislikes him, because Mulder is not a dutiful enough student. Patterson, however, follows Mulder's career, and holds him in very high respect. (In Grotesque, Scully mentions that Patterson's conflict with Mulder was 8 years earlier, yielding early 1988 or maybe late 1987. 1986 date for Mulder at the FBI Academy given in resume screen in Unusual Suspects.)

Using what he has learned from Patterson, Mulder writes a monograph on serial killers and the occult that helps catch Monte Props. (Pilot)

1988
Beginning this year, seven X-Files cases are opened in which people become deranged with the belief that a person is really a monster masquerading as a human. They each use a phrase something to the effect that the monster is "hiding in the light" so that most people do not see it. This same year, Greg Pinkas goes to work for VinalRight siding. He is present in each of the seven cases. Locations include Colorado, Texas, Missouri, Illinois, and Minnesota, among others. In fact, Pinkas is some sort of insectoid being that has the ability to cloud people's minds to not see him. Darkness reduces the effectiveness of this clouding. Pinkas creates zombies by injecting victims with a toxin at the backs of their necks. The final case is in Oak Brook, Illinois, in May of 1998. (Folie a Duex)

Late 1988
Mulder is assigned to the violent crimes section, where he is generally considered to be an expert analyst. (In Tooms, Mulder says he worked for three years with the FBI Behavioral Science unit, profiling serial killers. In Unusual Suspects, the resume screen indicated 1988 for his assignment to Violent Crimes. This matches well with his assignment to the X-Files in late 1991 or early 1992.)
Mulder is partnered with Jerry Lamana in the Violent Crimes unit. (Ghost in the Machine)

1988 or 89
Mulder is stationed in Washington DC. He initially offends his supervisor, Reggie Purdue, who later comes to greatly respect Mulder's intellect.
At this time (or maybe later) he rents apartment 42 at 2639 Hegal Place, Alexandria, Virginia, and acquires the telephone number (202) 555-0110. (Within)

In Mulder's first case in Washington DC, John Irvin Barnett, a New Hampshire native, kills seven people in the course of various armed robberies. A major task force is created, and Mulder's theory is that Barnett has a confederate in the armored car company, tipping him off to major cash shipments.
Barnett begins sending taunting notes to Mulder. Barnett is caught, but agent Steve Wohlenberg dies in a shoot-out. Mulder is convinced he could have saved Wohlenberg, although he acted by the book. Mulder never forgives himself. Barnett vows "I'll get you" to Mulder. (Young at Heart)

May 1989
The trio of paranoid conspiracy theorists known as The Lone Gunmen meet and begin working together. At a consumer electronics show in Baltimore, Byers enlists the assistance of Melvin Frohike and Langly to help a women who claims her three year old daughter has been kidnapped by a psychopathic ex-boyfriend. The two are competing hackers, and are each selling equipment to steal and descramble cable television service. (Unusual Suspects)