Charles Xavier is the mutant son of nuclear researcher Brian Xavier and his wife Sharon. As a young child, his father worked for a top secret research facility, perhaps tied into the Weapon X project that spawned such products as the mutant Wolverine. Even as a pre-adolescent, Xavier could use his telepathic powers to sense other people’s intentions and emotions. When Charles was still a boy, his father was accidentally killed in an atomic test. Shortly thereafter, Brian Xavier’s colleague, Dr. Kurt Marko, married Charles’s mother Sharon for her fortune. Marko’s son by a previous marriage, Cain, came to live at the Xavier Mansion in New York’s Westchester County, and, taking an immediate dislike to Charles, began bullying him. But Cain was often secretly beaten by his abusive father. On one occasion, Charles found himself experience the anguished thoughts of Cain after Cain had been beaten by his father. This was the first time that Xavier’s powers had fully opened another person’s mind to him. As Charles grew older, he learned how to control his telepathic powers. Xavier entered Bard College in Annandale-on-Hudson, New York, at 16 years of age, and earned his bachelor’s degree in biology in two years, followed quickly by degrees in genetics and biophysics at the same time from Oxford University. But immediately after finishing his work at Oxford, Xavier was drafted for World War II and sent to the Asian front. Wounded in battle, Xavier was recovering in a M.A.S.H. (Mobile Army Surgical Hospital) unit when he befriended psychiatrist Daniel Shomron. At this point of time he had been involved with a woman named Moira MacTaggart and who, during the war, had chosen to break their relationship. Released, he began aimlessly traveling about the Mediterranean, finally coming to terms with himself on the Greek island of Kirinos. Deciding to continue his travels, Xavier went to Cairo, Egypt, where he successfully defeated in battle the powerful telepath Amahl Farouk (later, the Shadow King), the first criminal mutant he had ever met. After his battle with Farouk, Xavier decided to make his life’s work the protection of humanity from mutants who used their powers in criminal ways as Farouk did, and the protection of mutants from persecution by humanity. From Egypt, Xavier went to Israel, probably to check out the new Jewish homeland, where Shomron introduced him to one of his patients, Gabrielle Haller, a survivor of the Nazi death camp at Dachau, who had withdrawn into catatonic schizophrenia.

Xavier used his mental powers to cure Haller of her condition, and the two became lovers, joining the Peace Corps. While in Israel, Xavier also met and formed a friendship fellow Peace Corps member and mutant who would be later known as Magneto (Magneto had at this time operated under the false identity of Erik Lensherr). Gabrielle Haller was captured by the Nazi war criminal Baron Wolfgang von Strucker and his HYDRA agents. Strucker tortured Haller into revealing the location of a cache of Nazi gold, the knowledge of which had been forcibly implanted in her brain at Dachau. Together, Xavier and Magneto rescued Haller, and Magneto took the Nazi gold with him to an unknown location. Xavier and Haller continued their affair. Xavier was unaware when he left Israel that Haller was pregnant with his son, whom she named David Charles Haller. Xavier continued to travel, and ended up in Tibet, where he met the alien known as Lucifer, who was bent on conquering the world (Lucifer was actually a guise adopted by the Dominus alien intelligence). Although he was successful in repulsing the alien attack, Xavier’s legs were crippled. While being nursed (in India?), he met the mutant Amelia Voght, with whom he developed a romantic relationship. Returning to Salem Center, he was joined there by Amelia. At some point during this time, Xavier and Amelia Voght had a falling out over philosophical differences, as she did not like his increasingly overwhelming need to be the self-imposed savior of mutant-kind. Furthermore, she did not like the idea of making kids into superheroes, and didn’t think that mutants should go public. It did not help that Xavier nearly used his powers to compel her to stay and adopt his POV. Again deeply depressed, he resumed graduate studies, eventually getting a Ph.D. in anthropology and another in psychiatry, as well as an M.D. degree. He continued his studies of mutation as well. Presumably, it was during this time that Xavier again met and redeveloped a friendship with Moira MacTaggart, now a research scientist in the field of mutations.

Although Xavier was still primarily a recluse over these years after his accident, at one point, a friend of Xavier’s from Bard, Prof. John Grey, brought his deeply disturbed 11 year-old daughter Jean to him for help. Xavier discovered that Jean was a superhuman mutant whose telepathic powers had emerged prematurely in reaction to stress. Xavier helped Jean recover from her trauma, erected psychic shields in her mind to prevent her from using her telepathic abilities until she had the necessary maturity for using them, and trained her over the following years in using her telekinetic abilities.

When the FBI launched an investigation of superhuman mutants, Xavier met with Fred Duncan, the FBI agent in charge of the investigation and proposed that he himself track down the superhuman mutants in the United States, train young ones to use their powers for humanity’s welfare, and report his progress to Duncan, who would keep Xavier’s involvement entirely secret. Xavier then found and befriended Scott Summers, who became Cyclops, the first of his students, whom he called “X-Men” (due to their extra powers), at his School for Gifted Youngsters, which was based in his Westchester County mansion. Over the next several years, Xavier also recruited the Iceman, the Angel, and the Beast, as well as the now-older Jean Grey, who took the codename of Marvel Girl. The first criminal mutant whom the five X-Men battled together was Magneto, who was now intent on world conquest. The U.S. military welcomed the X-Men’s help in battling Magneto when he captured the missile base at Cape Citadel, but eventually the X-Men were themselves regarded with suspicion by the government and general public, as prejudice and fear toward superhuman mutants continued.

Eventually Xavier learned through his telepathic powers that the alien Z‘nox intended to invade and conquer the Earth. Xavier believed that the Z‘nox could be defeated through psionic means. At the same time, the X-Men’s foe, the Changeling, learned he had a terminal illness and would not live more than six months. He contacted Professor X, wanting to do something to make up for his past crimes. Professor X had Changeling impersonate him so that he could go into hiding in order to focus all his attention and power on the Z‘nox invasion. Thus the Changeling, in the guise of Professor X, led the X-men for a considerable time. After several months, Changeling died after battling the inhuman Grotesk, although it would not be until many more months later, that Xavier would reveal himself alive as the alien invasion moved closer, and the X-men learned that the man who died was the Changeling. The X-Men were successful in stopping the Z‘nox invasion.

Later, Xavier recruited a number of new X-Men, including the Banshee, Colossus, Nightcrawler, Storm, and Wolverine, to help the other X-Men battle a “living island” called Krakoa. After this adventure, only Cyclops remained as Xavier began to serve as mentor for this second team of X-Men, which would grow over the years as other mutants joined and rejoined.

Xavier eventually met the Princess Lilandra of the Shi’ar Empire, with whom, in an as-yet unexplained way, he had forged a telepathic bond due to his massive use of psionic power in battling the Z‘nox. Xavier and the X-Men helped battle the forces of Lilandra’s mad brother D‘ken, and Xavier and Lilandra fell in love with each other. Xavier became her consort and went to live with her on the Shi’ar throne world for a time after she became empress. However, Xavier returned to Earth to deal with the dangers posed by the Phoenix Force, and he resumed his duties as mentor of the X-Men although he and Lilandra remained in love with each other. At one point, the X-Men disappeared while in outer space, and Xavier believed them to be dead, vowing never again to train young mutants for combat. Moira MacTaggart, however, persuaded him to continue to run the school to train young mutants how to deal with their powers. Xavier agreed and took on a new class of mutant students whom he called the New Mutants. In part he did so because he was subconsciously under the influence of a member of the alien Brood who had been implanted as an egg within his body, and was seeking superhuman victims. The growing Brood alien implanted within Xavier eventually took full control of his mind and transformed his body into that of a Brood. The Xavier-alien was defeated and captured by the X-Men, who had returned from outer space, and their ally, Binary (now, Warbird). Using Shi’ar science and cell samples taken from the human Xavier, MacTaggart and “Sikorsky,” the medic of the space pirate Starjammers, cloned a new body for Xavier which was slightly younger than his original one, and transferred his mind, now free from Brood control, into it. Xavier continued to mentor the New Mutants, although his relationship with the X-Men moved into more of an advisory capacity than true leader.

For years Xavier had been widely known as an authority on human mutation and as an advocate of peaceful relations between ordinary humanity and human mutants, although the public remained unaware that he himself was a superhuman mutant. Eventually, Xavier would grow a circle of mutant-activists that he would call his “Underground.” More recently, Xavier again served as a visiting professor at Columbia University, but was confronted outside class by a hostile group of students who objected to his pro-mutant sympathies. Xavier was forced to use his psychic powers to prevent himself from being attacked, but he was downed from behind by a hurled brick. Realizing that Xavier himself was a mutant, the students beat him nearly to death. Xavier was found by one of the Morlocks, a group of mutants who live underground, regarding themselves as outcasts. A leading Morlock, Callisto, had the Morlocks’ Healer use his powers to save Xavier’s life. Callisto warned Xavier that he would fully recover only if he avoided great physical or psychic strains on himself in the coming months. Shortly thereafter, Moira MacTaggart requested Xavier’s help in treating David Haller, Gabrielle’s son. Xavier learned that David was his own son, and Xavier and David were happily united after David finally emerged from his autistic condition and his normal personality had taken control of his mind. Over a number of months, however, David was returned to Muir Island for further treatment. Xavier did indeed undergo psychic strains and was slowly dying. He apparently began to regard Magneto as a possible successor to him as head of his school, and established a cover identity for him as his brother Michael Xavier. Xavier asked Magneto to look after the X-Men and to take over his School for Gifted Youngsters and the teaching of the New Mutants.

Just then Lilandra and Corsair, the Earth-born leader of the Starjammers, arrived by teleportation. Lilandra had been deposed as empress by her sister, Deathbird, and was now allied with the Starjammers as she sought to regain her throne. Lilandra and Corsair took Xavier back with them to the Shi’ar galaxy, where Xavier was fully healed by the advanced medical technology of the Starjammers, eventually restoring his ability to walk. However, he was unable to return to Earth since the Starjammers’ special hyperspace drive for intergalactic travel was damaged (without that drive a journey to Earth even through space warps would take centuries), and the Shi’ar stargates were all now heavily defended against Starjammer intrusions. Hence Xavier remained aboard the Starjammers’ starship, separated from the X-Men and the New Mutants (although, at one point, he had one adventure with the New Mutants), but reunited with Lilandra, whom he loves.

At some point, however, Xavier, Lilandra, and the Starjammers were captured and impersonated by a warrior of the shape-shifting Skrull alien race in the beginnings of a Skrull-Shi’ar war. Then, using the X-men as allies, the Skrulls staged a coup to restore “Lilandra” to her throne. Xavier nevertheless remained in the Skrull’s thrall until the X-men and Deathbird discovered the Skrull’s plan and defeated them. Xavier helped defeat the Skrulls, and left with the X-men, returning to Earth as Lilandra resumed her empress duties. On Earth, Xavier and the X-Men arrived in time to fight the Shadow King, who had since taken over MacTaggart’s Muir Island research facility, including David Haller. Although they defeated the Shadow King, Xavier was wounded once again, leaving him without the use of his legs.

Xavier continued to stand by his X-men, at one point he was forced to battle Magneto again. This time, Xavier reached into Magneto’s mind to shut it off, placing Magneto in a coma but preparing the way for a split personality to emerge in his own mind, which would eventually develop into “Onslaught.” After several series of secret ploys and machinations, Onslaught finally emerged physically, creating a body for himself out of psionic energy and stripping Professor X of his mental powers in the process. He quickly began taking steps to take over the world, and kidnapped Nate Grey, the X-Man, and Franklin Richards to absorb their psychic and reality-warping abilities for himself. In the meantime, Onslaught battled the combined might and minds of the X-Men, Fantastic Four, Avengers, and their allies. Ultimately, Onslaught was defeated by being physically absorbed by the assembled heroes, who seemingly sacrificed themselves. Once Onslaught was finally defeated, Xavier turned himself in to the U.S. government for the crimes of his “other self,” despite the fact that he remained powerless. He was put into custody and watched over by the mutant-hating Bastion. Bastion subtly tried psychological torture on Xavier, trying to learn all of the X-Men’s secrets, although he was ultimately unsuccessful. About the same time, Bastion launched a full-scale attack on the nation’s mutants in the so-called Operation: Zero Tolerance. The X-Men thwarted Bastion’s plans, but Professor X had disappeared. Xavier reappeared, leading a group dubbed the Brotherhood of Mutants. The X-Men confronted the team, learning that this Xavier was in reality a construction of Cerebro, a device of Xavier’s that had gained intelligence. Cerebro had captured Xavier in order to take his place. During the ultimate confrontation, the X-Men’s ally, the robot Nannite named Nina, restored Xavier’s powers and he destroyed Cerebro (Professor Xavier, with the help of the X-Men’s Beast, has since created a new mutant-tracking computer system, calling it Cerebra). Xavier returned with the X-Men as their mentor and leader.

When the X-Men returned from a space-faring mission, they inadvertently returned to Earth with the alien Skrull named Fiz with them. Xavier discovered and attacked Fiz, but Fiz explained he wanted to join their team. The alien helped the X-Men track down and defeat their enemy Apocalypse and his mutant Skrull allies. After the battle, Xavier agreed to leave Earth with Fiz and the mutant Skrulls, whom Xavier dubbed Cadre K, in order to find a new homeworld for them and to train them in the use of their powers. Cadre K soon found a new role, that of freedom fighters, championing for mutant rights within their Empire. During a time that Earth was declared a penal colony for unwanted alien criminals, Xavier and Cadre K embarked on a plan to defeat the true cause of Earth’s plight: the alien Kree who were searching for revenge on Earth for its part in its decimation as an Empire. The Cadre helped Earth battle the Kree, and Earth ultimately thwarted the Kree’s plans. Afterward, Professor Xavier elected to remain on Earth, proud of the team he forged. More recently, Xavier, along with his protég ́s Beast, Wolverine, Cyclops, and Jean Grey, re-opened his school for mutants, now called Xavier’s Institute of Higher Learning, to the mutant population at large. They began to recruit more mutants, training and educating them to help them cope with their powers. Xavier now helps to educate and train dozens of young mutants, many severely disfigured or requiring specialized training and technology.

When Xavier’s mind witnessed the genocide of the mutants of the island of Genosha, the villain behind the attack revealed herself to the X-Men as Cassandra Nova. Xavier claimed her to be his genetic twin. Cassandra invaded the school but was seemingly defeated by Xavier and Emma Frost. Almost immediately afterward, Xavier publicly revealed his mutant nature and the true nature of his school. Despite the resulting controversy and rioting and attacks outside the school, Xavier contacted Lilandra and left for a vacation in her empire. The X-Men soon discovered that Cassandra had switched bodies with Xavier and was wreaking havoc in the Shi’ar Empire. Xavier, instead, was actually stuck in Cassandra’s diseased body, slowly losing his mind to a combination of terminal illnesses. Cassandra returned to Earth with the full might of the Shi’ar Empire at her disposal, intent on destroying Earth. Jean Grey coaxed Xavier’s mind out of the dying body, hoping that if she could contain his entire psyche and allow the body to die, Cassandra would be deprived of a host to inhabit. Jean used the Cerebra device to transfer pieces of Xavier’s psyche into the mind every mutant in the world. Cassandra (in Xavier’s body) responded by reintegrating Xavier’s mind into his body with her, believing this would let her take control of all mutants. The mutant Xorn then confronted her, using his abilities to heal others. The ultimate effect was to heal Xavier in mind and body, even to the point of being able to walk again, and Cassandra was destroyed. Xavier is now active as an x-Man himself, while engaging in teaching, covert operations and the X-Corporation