Charles Francis Xavier was the mutant son of wealthy nuclear researcher, Dr. Brian Xavier, and his wife, Sharon Xavier-Marko.While gestating in his mother's womb, Charles' twin was recognized by Charles as an evil presence and he preemptively tried to kill it with his nascent psychic abilities, causing the fetus' miscarriage. After Dr. Xavier's death in an accident, Sharon married his colleague Dr. Kurt Marko who brought his son by a previous marriage, Cain Marko to live in their ancestral mansion. Dr. Marko favored the gentle, smart Charles over his own son, which led to Cain constantly bullying Charles and Dr. Marko secretly beating Cain. Sharon married Dr. Marko because she believed that it would be best for Charles.
Charles' telepathic powers began emerging when he was still a boy, around ten, and, as he grew older, he learned to control them. Due to the immense psychic energies emanating from Charles' head, he became bald at a young age. With his powers, Charles had discovered that Dr. Marko cared only about his mother's money, admitting that he was jealous of Dr. Xavier's wealth. Dr. Marko quickly grew neglectful of Sharon, driving her to alcoholism, and abused both Sharon and Cain. Charles linked his mind to his mother's in an effort to share the abuse with her and alleviate it. Charles, on one occasion, found himself experiencing the anguished thoughts and emotions of Cain, after Cain had been beaten by his father, which only led to Cain becoming more aggressive toward him and Charles feeling Cain's pain firsthand, but the inexperienced young Charles could not control or end his contact with Cain's mind at this time. Sharon died shortly thereafter of a broken heart, leaving Charles to live with his step-father and abusive step-brother.
Later, a fight erupted between Cain and Dr. Marko, causing some of Dr. Marko's lab equipment to explode. Mortally wounded, Dr. Marko dragged the two children out before dying, begging forgiveness for not saving Dr. Xavier when he had the chance, and telling Charles to keep his powers secret from Cain. Cain was standing over them and heard of Charles' gift, which led him to believe that Charles had invaded his thoughts deliberately. From then on, Cain regarded Xavier as his enemy.
Powers and Abilities
Professor Charles Xavier was an Alpha-Level Mutant, an Omega Class Telepath, was said to possess the most powerful brain in existence, to be the world's greatest telepath and possesses vast psionic powers:
Telepathy: Able to read minds and project his own thoughts into the minds of others within a radius of 250 miles (on Earth). With extreme effort he can greatly extend that radius. When synched with Cerebro or Cerebra, he can connect to every mind on a planet. After he was thrown into the M'Kraan Crystal, it not only restored his mutation, but made his telepathy more powerful than it has been previously, thereby making him the world's most powerful telepath once again.
- Telepathic Illusions: ability to create realistic telepathic illusions and cause people to experience events which are not actually occurring.
- Telepathic Cloak: can mask his presence from being detected by others. His abilities can at times go undetected or be counteracted by other more powerful telepaths depending on their level of skill in using their own psi abilities. He can extend these defenses to others around him as well.
- Mind Link: ability to develop a mental link with any person which remains as a connection to that individual.
- Telepathic Camouflage: ability to mask himself, and other peoples' presence from those around him. Can telepathically disguise himself, making his appearance to those around him quite different (changing the appearance of clothing, as well as more involved disguising).
- Mind Blast: ability to place large amounts of information in another's mind.
- Mind Control: ability to control the minds of others upon mere concentration. This power can allow him to completely shut down several people's minds, making it appear as if time has stopped.
- Mind Possession: ability to possess the mind of another, and use that being's body as his own.
- Mind Alteration: ability to alter the minds of others by force of will.
- Mental Amnesia: ability to cause loss of particular memories or total amnesia in another person or group of people.
- Psionic Shield: ability to erect a psychic shield for protection of himself and of other minds, so that he can prevent the free access to the conscious and subconscious mind of anyone.
- Psionic Blasts: can project psionic force bolts which have no physical effects but which can affect a victim's mind so as to cause the victim pain or unconsciousness and can even kill an adversary.
- Astral Projection: ability to Astral Travel and communicate with others astrally through his own will, or through contact with the thoughts and memories of others. In the astral realm, he can use his powers to create "ectoplasmic" objects. He cannot engage in long range astral projection on the earthly plane.
- Mental Detection: can sense the presence of another superhuman mutant within a small but as yet undefined radius of himself by perceiving the distinctive mental radiations emitted by such a being.
- Mind Transferal: able to transfer both his mind and powers into other host bodies if his own physical body could be somehow killed.
- Absorb Information: ability to quickly process and store information, by mental transference.
Professor X formerly also possessed low-level telekinetic abilities, though these seem to no longer exist. They seem to be part of his genes however, as Cassandra Nova has telekinetic abilities and is basically a clone of Xavier.
- Genius Intelligence: A natural genius, Xavier is a leading authority on genetics, mutation, and psionics. He possesses considerable expertise in other life sciences. He is highly talented in devising equipment for utilizing and enhancing psionic powers. Xavier is also quite the masterful tactician and strategist, effectively evaluating situations and devising swift responses; he has, on numerous occasions, even fashioned long-term operations as complex as those of adversaries such as Sinister, Magneto, and Apocalypse.
- Military Training: Charles served in the United States Military, secretly employing his abilities to specialize in search and rescue missions. 
- Expert Fighter: In his travels in the East, he became a proficient hand-to-hand combatant and gained knowledge of pressure points.
Strength of a normal man his age and size who engages in moderate regular exercise, mostly in his upper body.
- Dark Side: Xavier was shown to have a dark side, a part of himself that he struggles to suppress. Perhaps the most notable appearance of this was the entity Onslaught, which was a physical manifestation of that dark side. Also, Onslaught was created in the most violent act Xavier claimed to have done: Erasing the mind of Magneto. Once the X-Men fought images of the original team, which had been created by what Xavier said was his "evil self ... who would use his powers for personal gain and conquest," which he said he was normally able to keep in check.
In other instances, Xavier was shown to be secretive and manipulative. During the battle against Onslaught, the X-Men found Xavier's files, the "Xavier Protocols," which detail how to kill many of the characters should the need ever arise, such as if they went rogue. Also it was revealed that when Xavier realized that the Danger Room had become sentient, he kept it trapped and experimented on it for years, an act that Cyclops called "the oppression of a new life" and equated to humanity's treatment of mutants. Later still, a de-powered Xavier was forced to admit that he had sent a group of hastily trained young mutants and carelessly sent them to Krakoa to save the original X-Men, resulting in their deaths. Because one of the mutants was Cyclops' brother Vulcan, Xavier erased Cyclops' memory of the event. He further manipulated the rescue team of new X-Men by making them think the meaningless noises the island made were intelligible speech—evidence that the island was alive—to match the new memories he had given Cyclops.