His fascination with the paranormal stems from a childhood incident -- his sister Samantha disappeared from their home in 2790 Vine Street, Chilmark, Mass. (pop. 650) when he was 12 and she was 8, in the middle of the game of Stratego. Mulder claims she was abducted by aliens; during regressions he recalled hearing his sister's cries for help, and a bright light which kept him paralyzed and told him that his sister would be all right [Conduit]. This memory differs from a dream Mulder experienced one night [Little Green Men]. Mulder has come in contact with an alien hybrid who claimed to be Samantha and an alien bounty hunter who told him that his sister was alive. He has vowed to continue his search for her [Colony/
Mulder's early meteoric rise at the Bureau enabled him to make high-placed friends in Congress -- one of them being SETI proponent and influential senator Richard Matheson [Little Green Men]. These contacts had kept him from retribution from higher-ups, although they assigned him a partner, with the tacit idea of discrediting what he does so that he can be dismissed. However, Mulder picked up a somewhat vacillating ally in a mysterious covert individual known as Deep Throat [Deep Throat, Fallen Angel, Eve, Young at Heart, E.B.E., Erlenmeyer Flask].
Deep Throat was killed by an equally mysterious covert opponent (Crew Cut Man) during an attempt to rescue Mulder. Mulder confirmed his burial at Arlington "through eight-power binoculars from a thousand yards away" [Little Green Men]. But he acquired a second "deep information" associate, someone who is referred to as X [Sleepless]. This mysterious man had been less helpful to Mulder than his dead colleague, although he did provide information about Mulder's mother and the Cigarette-Smoking Man [Talitha Cumi]. The Cigarette-Smoking Man had killed X on Mulder's doorstep [Herrenvolk], but not before leading him to an assistant to the Special Representative to the Secretary General of the U.N. [Herrenvolk], who has been able to help him [Tunguska]. Mulder has also been told by an unknown individual that he has "a friend in the FBI" [The Host]. This friend has now been identified to be Assistant Director Skinner [Paper Clip].
At the end of Season 1, the X Files division was shut down and Mulder was reassigned to wiretap surveillance [Little Green Men, The Host]. He also reluctantly acquired a new partner, Special Agent Alex Krycek [Sleepless, Duane Barry, Ascension], a younger agent who purported to be a believer, not only in Mulder's ideas but in Mulder himself. Mulder's days in this mind-numbing duty were numbered, however. Assistant Director Skinner obliquely acknowledged that the X Files department served a valuable purpose in dealing successfully with the Bureau's oddball cases [The Host] and was bringing to light information that other covert parties would prefer to keep buried [Ascension]. Following the disappearance of Mulder's former partner Dana Scully, Skinner officially reopened the X-Files [Ascension].
At the end of Season 2, Mulder came into possession of a Defense Department classified, Navajo-coded electronic document that purported to be the records of events surrounding a covert government operation from 50 years ago. Opponents tried to discredit him by adulterating his drinking water with a substance making him progressively violent. His father, who was somehow connected to the operation, was murdered, with Mulder as the prime suspect. Going into hiding with Scully, Mulder ended up in New Mexico investigating evidence that proved the validity of the secret document. He was found out by Cigarette-Smoking Man, who attempted to kill him [Anasazi]. The disk of information is now in CSM's hands [Apocrypha].
Mulder recovered through the intervention of the Navajo and returned to the East Coast to peruse his dead father's effects, finding a mysterious 1970s photo of an interesting group of men [The Blessing Way]. Returning to D.C. he met up with Scully and received help from the Lone Gunmen and one of the photographed men to discover the secret location of the files concerning the covert operation: medical records and tissue samples from children vaccinated in the 50s and 60s, including Scully's. On the run from their opponents, they received help from Skinner, who negotiated a truce with Cigarette-Smoking Man for the agents' reinstatement and relative safety [Paper Clip].
At the end of season 3, in the search for another group of alien clones, Mulder recovered a weapon said to be the only device able to kill the clones, and faces again a morphing alien who supposedly destroyed clones of his sister who were living on earth. He thought he had killed the morphing alien, but the alien survived and followed Mulder to a Canadian farm, where young worker-drone clones who could not speak, one group of which were clones of a young Samantha, kept bees for an alien project. But Mulder was unable to learn the true nature of the project, or bring back one of the Samantha drones [Herrenvolk]. The bees have been shown to transport a mutated strain of smallpox [Zero Sum].
At Krycek's instigation, Mulder (and Scully) investigated the illegal importing of rock from the Tunguska area of Siberia where a meteorite had reportedly fallen to earth. The rock contained an exterrestrial life form. Mulder and Krycek traveled to Tunguska, where Mulder was captured and infected with the life form by Russian "researchers". He was able to escape and return to the United States [Tunguska, Terma].
In the final episode of 4th season, Mulder apparently has committed suicide because of yet another orchestrated ruse about aliens on Earth [Gethsemane].
At the end of season five, Mulder's work, all of the X-Files, were burned in his private office at the FBI Headquarters by the Cigarette-Smoking Man who first removed Samantha Mulder's file [The End]. The X-Files were apparently destroyed because a link in solving them all had allegedly been found through the mind reading abilities of a 12 year old boy. Solving all of the X-Files would be a threat to the consortium's planned project involving extra-terrestrials and involving the Cigarette-Smoking Man...
On the beginning of season six, Mulder and Scully are being reprimanded for their conduct and report presented based on the events of the movie. They are taken off the X-Files [The Beginning], which are given to agents Spender and Fowley. Mulder and Scully no longer report to Skinner. They are placed under the supervision of Assistant Director Kersh, a mean spirited and somewhat devious man with an agenda that may put him in with the cigarette smoking man and the consortium. Mulder and Scully are demoted into doing back ground checks on people and the idea is to force Mulder into quitting the FBI.
Mulder won in his exposure of the show's main conspiracy but in doing so, he still has no direction in searching for his sister and his exposure of the conspiracy only ended up widening the power base that the cigarette smoking man has, not to mention the new clout given to Alex Krycek and Diana Fowley [Two Fathers, One Son].
At the end of season six [Biogenesis], Mulder was hospitalized for a numbing brain disorder while Scully was off to search for clues to try and explain the origins of a mysterious artifact found off of the west coast of Africa. This artifact with a hybrid of scientific and supposedly religious meaning and the thing responsible for Mulder's condition are somehow explained in "The Sixth Extinction" "The Sixth Extinction II: Amor Fati". Mulder's mother commited suicide by overdosing by Diazepam [Sein Und Zeit]. Mulder also finally found out the fate of Samantha when he learns that after she was kidnapped and subjected to testing, a spiritual intervention came to her rescue and transported her soul to heaven [Closure]. With that preoccupation removed, Mulder focused on a greater truth: the confirmation of alien life. Unfortunately, he himself has become the X-File [Requiem], and the task of saving him falls on the shoulders of the only person he can trust - Scully.
Mulder is known around the Bureau by the nickname of "Spooky" [Pilot, Young at Heart] both because of his uncanny ability to process information and leap ahead to logical conclusions, and because of his interest in paranormal phenomena. "He is considered a loose cannon, a person who is maybe wasting time and money, and also his expertise, on an area the Bureau thinks has very little value." [Carter, Starlog]. Due to an incident on one of his first Bureau assignments (a fellow agent was killed) [Young at Heart], he eschews following investigations "by the book", opting instead for his own instincts and methods. He keeps notes for his field reports in a handwritten journal [Born Again]. His favorite alias is George Hale [Little Green Men; Sleepless]. When he wrote an article in "Omni" about the Gulf Breeze sighting, he used the name M.F. Luder. Jose Chung refers to him as "Reynard Muldrake", Reynard meaning Fox. He also uses the name "Marty" when contacting the blood banks , and calls under the same name certain phone sex lines' numbers [Small Potatoes]. In "The Pine Bluff Variant" he uses the name "Mr Kaplan", when staying in a motel undercover. In "The Unnatural" he calls himself "Fox Mantle".
It is believed Mulder doesn't "have a life", as we have seen little of his off-duty activities. However, some of this may stem from a relationship he had at Oxford ten years ago with a woman who is now with Scotland Yard (Phoebe Green) [Fire]. He apparently was in love with her but she not with him. With the dissolution of the X-Files division, however, Mulder may have been trying to revive his social life; an answering machine message berated him for missing a lunch date [Little Green Men].
Mulder's birthdate is Oct. 13, 1961 [Paper Clip] and his birthplace is Chilmark, Massachusetts [Dreamland II]. His parents have been divorced. His father, Bill, worked in an unknown capacity for the State Department, and was murdered by Krycek before telling Mulder about secrets in his past [Anasazi]. Before his death, he lived on Martha's Vineyard, at West Tisbury in a house he gought after the divorce. Mulder's mother, Tena, confirmed that Samantha had been kidnapped to insure her father's silence about his covert activities [Paper Clip]. She lives in Connecticut.
He has a fear of fire [Fire], which may have been conquered during his rescue of the children of British MP Sir Malcolm Marsden (who also happened to be Phoebe's latest fling), and of insects [War of the Coprophages]. He is also a fan of the National Aeronautics and Space Administration (NASA) [Space] and classic Star Trek [Dreamland II]. He has a habit of eating shelled sunflower seeds (a habit he shares with his father [Aubrey]) or pistachio nuts, and making droll comments which X-Philes have come to note as "Mulderisms".
Mulder says that he is red-and-green colorblind [Wetwired], but it seems to be just an apology for wearing moderately wild ties to work, and seems to be a New York Knicks fan in basketball [Beyond the Sea, Little Green Men, Clyde Bruckman's Final Repose] as well as a Washington Redskins in football [Irresistible]. He laments with Deep Throat that they could never catch a game together. Judging from the fact that he appears to use football tickets as currency [Conduit], one wonders if he ever actually gets to a match. He knows about football from when he was quite young, discussing the 1968 Superbowl with Colonel Budahas [Deep Throat]. When bored, or waiting for informants, he likes bouncing a ball in his apartment. Mulder is also capable of playing bowling [Elegy]. He also keeps himself physically fit by running [Pilot, Deep Throat, Blood, Humbug, The Pine Bluff Variant (kinda)] and swimming [Duane Barry]. Baseball is another of his favorite ways of relaxation [Blood, Home, The Unnatural] and he played right field when he lived in the Vineyard. He appears to have a fondness for classic rock [Beyond the Sea, GenderBender] and classic science fiction movies [Tooms, Erlenmeyer Flask, War of the Coprophages], and iced tea seems to be his nonalcoholic beverage of choice [Tooms], along with orange juice [Chinga]. He has nothing against pizza [Sein und Zeit]. He was a fan of the television show "The Magician" as a child [Little Green Men].
There are suggestions that Mulder has an interest in pornography -- in "Jersey Devil", we see Mulder looking at the centerfold of some "men's magazine" talking about how the woman claims she was abducted by aliens; in "Beyond The Sea" Scully remarks that she hadn't seen Mulder that excited since she caught him going through the Adult Video News; "Blood" mentions a subscription to Celebrity Skin, he appears to be viewing a porno video in "3", "One Breath" and also in "Chinga" (Alien Probe), and he makes comments about a video he purchased (not a porno video) in "Nisei" and asks if [communicator] receives Playboy Channel in "Pusher". Also, he tells Frohike in "Paper Clip" that he'll have to wait a little longer for Mulder's video collection. In "DPO", Mulder picks up a magazine, turning it round to look at the centre-fold. "I'm surprised you haven't already read that issue," Scully comments. Mulder says he has, but his copy didn't have a photo stuck between Miss April and Women of the Ivy League. Another one in "Kill Switch": if the VR vision thing did derive in some way from Mulder's subconsious, then those buxom nurses are presumably straight off one of his videos. Also, being tied down to a hospital bed and having blonde busty nurses rubbing his body counts as a "good dream." In "All Souls" Mulder is seen going into a cinema that is showing "A Decade of Dirty Delinquents." In "The End": Mulder asks Gibson Praise "What's wrong with Baywatch?" "You have a dirty mind", the boy replies. In "Dreamland" Mulder sleeps to the soft-core SIZL station (and mumbling about Scully in his sleep). In "Dreamland II" there is a copy of "PlayPen" magazine in his bedroom. He also appears to call sex hot lines [Small Potatoes]. As a psychologist, he favors using hypnotic regression as a psychological healing tool, and hates the unnecessary use of medication [Born Again]. [Season 1, 2, 3, 4, 5, 6, 7, 8, Movie]
Special Agent Fox Mulder
Name: Fox William Mulder
Badge number: JTT047101111
Agent number: 22791
Weight: 170 lb
Hair color: Brown
Eyes color: Green
Blood type: AB negative
Birthdate: October 13, 1961
Birthplace: Chilmark, MA
Social Security no.: 123-32-1321
Address: 2360 Hegal Place Alexandria, #42, VA, 23242
Phone no. (202) 555-9355, (202) 555-0199 
Father: William "Bill" Mulder
Mother: Tena Mulder
Siblings: Sister - Samantha Ann Mulder (born January 22, 1964, disappeared November 27, 1973 - X-file number X-42053)
Education: Oxford University (psychology) 1982, Quantico FBI Academy 1984