HISTORY: The X-Men is an organization of superhumanly powerful mutants that was founded by Professor Charles Xavier for two purposes: first, to train such mutants in the uses of their superhuman powers, and second, to serve as a combat team that could defend humanity against attacks by superhumanly powerful mutants who use their powers for criminal ends, as well as against other threats

The civilian identities of most of the X-Men are unknown to the public. In their civilian identities the X-Men are officially students at or alumni on Professor Xavier's School for Gifted Youngsters. The School, where the X-Men are based, is housed in Charles Xavier's mansion at 1407 Graymalkin Lane, Salem Center, Westchester County, New York. The Manson serves as the X-Men's base of operations, training center, and living quarters. Although the true identities of two of the X-Men's founding members, the Angel and the Beast, have become public knowledge, they have apparently managed somehow to conceal the fact that they attended Xavier's school from public awareness.

Virtually every member of the X-Men is a superhuman mutant. There have, however, been exceptions, such as the Mimic, who could duplicate the superhuman powers of mutants, and Longshot, an artificially created, genetically engineered humanoid from another dimensional world.

Charles Xavier is himself a superhuman mutant who, as a young man, used his telepathic powers to battle various menaces. After being crippled in an encounter with the alien Lucifer. Xavier led a reclusive life as an academic and a scientific researcher. He was contacted to help Jean Grey, who was then still a child, and was unable to control her newly emerged mutant telepathic abilities properly. Xavier used his own psychic abilities to erect psionic blocks in Grey's mind to prevent her from using her telepathic powers until she was mature enough to deal with them. Over the following years Xavier worked with Grey to develop her mutant telekinetic abilities.

Xavier expected that normal human beings would eventually come to fear and persecute the growing number of superhuman mutants. Xavier learned from news reports of an adolescent mutant who nearly became the victim of mod violence after he publicly displayed his superhuman power. This mutant, was being investigated by Fred Duncan, an agent of the Federal Bureau of Investigation. Xavier contacted Duncan and told him of his intention to find young superhuman mutants and train them in the uses of their power for the benefit of humanity. Duncan and Xavier agreed to cooperate with each other. This cooperation between Xavier and the federal government lasted for several years, but Xavier put an end to it when he realized that the government's attitude towards superhuman mutants was beginning to turn hostile. Xavier and his student Katherine Pryde, an expert with computers, have seen to it that government records about the X-Men dating from the years of cooperation with the F.B.I. have been destroyed. Duncan was once reported dead, but this report may be untrue. His current activities, if he is still alive, are unknown.

Using Duncan's files, Xavier deduced that the young mutant Duncan was investigating was Scott Summers. Xavier sought out Summers and enlisted him as the first of his X-Men, Cyclops. Xavier called the team "X-Men" because each one had an "extra" power that normal people lacked. (Not so coincidentally, of course, "X" was also the first letter of Xavier's last name, and he himself took the code name "Professor X

Over the following months Xavier recruited three more superhuman mutants and began training them in the use of their powers: Robert Drake, who took the name Iceman, Warren Worthington, the Angel, who had already begun a career as a costumed crime fighter, and Henry P. McCoy, a college student who became known as the Beast. Xavier then invited Grey, who had already became quite adept in the use of her powers due to his training, to join the team; she took the code name Marvel Girl.

Xavier's first five students were all adolescents when they joined the X-Men. Xavier was apparently not opposed to inducting to inducting an adult into the X-Men, and in fact offered membership in the team to the adult Blob, who rejected it. Afterwards, Xavier seemed uninterested for years in recruiting new member for the X-Men. Calvin Rankin, the Mimic, insisted on joining the group, although he resigned soon afterwards. Two other young mutants, Lorna Dane, alias Polaris, and Scott Summers' brother Alexander, alias Havok, became reserve member of the X-Men, although it is unclear whether they actually became members of Xavier's school.

Professor Xavier School for Gifted Youngsters is a fully accredited institution of learning, and Xavier provides his student with the equivalent of a high school and college education in traditional academic subjects while also training them in the uses of their mutant powers.

The X-Men first publicly appeared as a team when they first battle the powerful mutant Magneto, who had captured the American missile base at Cape Citadel. The American military was grateful to the X-Men for driving from the base, and initially the X-Men were publicly regarded as heroes. However, fear and distrust of mutants continued to rise, reaching one of its first peaks, perhaps, at the time that Bolivar Trask publicly revealed the existence of his mutant-hunting robots, the Sentinels. Over the last several years the X-Men have been publicly regarded with suspicion, and have been unjustly accused of various crimes. Indeed, since the end of Xavier's cooperation with the F.B.I., the X-Men have officially been regarded as outlaws.

Requiring seclusion while he prepared to deal with a forthcoming invasion of Earth by the alien Z'nox, Xavier had the mutant Changeling impersonate him in order to supervise the X-Men in Xavier's absence. However, the Changeling, as Xavier, died heroically in action, and Xavier felt obliged to continue the pretense of his death. Of the X-Men, only Marvel Girl knew that Xavier was still alive, and she was sworn to secrecy by Xavier. Duncan had the X-Men disband briefly, but the team later reunited, and finally, Xavier revealed to the four male X-Men that he was still alive. The X-Men then assisted Xavier in defeating the Z'nox.

Years later, the original team of X-Men were trapped by the mutant entity known as Krakoa the living Island. Xavier therefore was obliged to recruit new X-Men to rescue his original team and to defeat Krakoa. The new recruits came from various countries: the Irish Banshee, the Soviet Colossus, the German Nightcrawler, the African Storm (who was born, however, in the United States), the Japanese Sunfire, and the American Indian Thunderbird. Most of these new members were adults, and were already quite adept in using their superhuman abilities. These "new" X-Men, together with the original members, dealt successfully with Krakoa, and all returned safely to Xavier's mansion. Soon thereafter all of the original X-Men left the team except for Cyclops. Sunfire also quit the group, and Thunderbird was soon killed in action, but the other new members stayed in the team

A manifestation of the phoenix-force, a sentient energy being, adopted the form and persona of Jean Grey, and, as Phoenix, joined the team only to sacrifice its existence in Grey's form months later. The Banshee left the X-Men due to injuries. New members who joined were Katherine "Kitty" Pride, an adolescent known a Shadowcat, who was the team's youngest member at that time, the X-Men's former enemy Rogue, and Rachel Summers, the second team member to be known as the Phoenix, who comes from the future of an alternate time line
At a time when Xavier believed that the X-Men might have been killed, he decided to form a new team of adolescent superhuman mutants, whom he would train at the school in the use of their powers; but whom he would not send into combat. The members of this team, the New Mutants, have nonetheless often found themselves in battle through circumstances, and have frequently aided the X-Men in combat.

The X-Men's greatest opponent, Magneto, has reevaluated his life and beliefs acting as the X-Men's ally. When Xavier was on the brink of death due to severe injuries, he persuaded Magneto to take his place as head of his school in his absence. Xavier was teleported off Earth to the Shi'ar Galaxy by his lover, the Shi'ar Princess Lilandra Neramani, and his ally Corsair. Xavier has by now fully recovered, thanks to Shi'ar medical science, but he has so far been unable to return to Earth. Magneto, under the alias of Michael Xavier, Charles Xavier's alleged cousin, now runs the school and instructs the New Mutants. Magneto is also now a member of the X-Men, although Storm is now the team's actual leader
Xavier's original five students, now all adults, still do not trust Magneto and are dismayed that the current X-Men have allied themselves with him. As a result, Xavier's five original students have formed their own organization, X-Factor, in order to find and train superhuman mutants.

Recently, Colossus, Nightcrawler, and Shadowcat have all had to take leaves of absence from the X-Men due to severe injuries. Reserve member Havok has become an active member of the team, and three new recruits have joined as well: the Dazzler, Longshot, and Psylocke