Jean Grey's History
Jean Grey was a normal teenager with a normal family until her mutant powers manifested. Her telepathy caused her to suffer from terrifying hallucinations of a giant, wild, flaming raptor, and she was held in a mental institution presumably for observation and testing before she met Professor Charles Xavier, who offered her a place among his X-Men, along with a chance to learn to control her powers and avert the upcoming mutant/human war.
X-Men
Jean became Xavier's second student, after Cyclops, and began to learn a great deal about her powers. Jean proved to be outgoing, yet responsible and mature.
Jean developed a relationship with Wolverine, the newest X-Man, and slept with him. Unbeknownst to her, Wolverine was secretly working for Magneto and his Brotherhood, and was plotting to kill Charles Xavier. Wolverine admitted to her that he first joined the X-Men to act as a mole and assassin for Magneto, and, repulsed, Jean dumped Wolverine.
Fire and Brimstone
Jean was possessed by a so-called Phoenix God and became nearly insane, but escaped its grip. The Hellfire Club believed that Jean was the perfect host for their God, yet Xavier claimed that Jean's Phoenix powers were the result of Jean's own mutation growing, as Jean was a powerful mutant, yet lacked control. Jean briefly believed the Phoenix to be an intergalactic demon bent on destroying the world through her before accepting Xavier's explanation that there was no Phoenix entity but just her evolving powers. Thor questioned Xavier's logic.
Jean Grey's powers would often emanate as a halo in a fiery bird-like form and she often had difficulties controlling her ever-growing powers.
Church of Shi'ar Enlightenment
Having lost his government funding, Xavier was unable to continue funding his X-Men. Almost too perfectly, a group of new religious followers known as the Church of Shi'ar Enlightenment, led by Lilandra Neramani, approached Xavier with a proposal: they would fund his endeavor if they were allowed to observe Jean Grey, who they believed may have a connection to their God. Xavier and Lilandra were attempting to uncover if Jean was the avatar and/or host of the Phoenix God. The Shi'ar believed the Phoenix God was held captive by an alien armada that utilized their own technology and the powers of the Phoenix itself to create a planet that it would be imprisoned in; that planet, the Shi'ar believed, was Earth. They believed that once the Phoenix had awoken, she would make Earth a utopia of Mutant/Human harmony and craft the universe into a paradise.
Jean refused to believe that she was the Phoenix. But she willingly subjected herself to tests to determine if she was the Phoenix. But the questions turned out too much and the Phoenix awoke - in an evil form Aka:Dark Phoenix. She taunted Lilandra for trying to see the realm of a god and prepared kill to Lilandra, starting with her non-essential organs then the essential. Xavier tried to stop her but the Phoenix was more powerful and tried to melt his brain until he admitted that he loved her, snapping Jean back to normal, but he shut off her brain temporarily. When she woke up, Lilandra's assistant Gerald confirmed that her subconscious manifested a false Phoenix (albeit he was telling a lie, she was in fact the host of the Phoenix god), it left Jean to think she was insane, her depression causing her to make four strange goblin-like creatures that seem to be part of he.
Merged with the Phoenix
As Xavier was about to be killed by Apocalypse, Jean called out to the Phoenix Force for help. Merging with the powerful entity again, Jean blasted Apocalypse from behind. When he got up, he sensed great power in her, both mutant and not, intending to take it. Phoenix merely taunted him, saying he was facing a god and unleashed a small fraction of her power on him, melting his armor. He feigned defeat then struck back, so she decided to unleash her full might against him, causing pain that made him beg for her to stop; she complied. Defeated, Apocalypse's true form, Sinister, was revealed. As the X-Men and Fantastic Four gathered, she proclaimed she was not Jean. But she still had strong feelings for them, but saw there was much work to be done. She flared her anger at Xavier, pointing out the damage that he caused: "You set the mutant cause back by a hundred years." She expected him to "start over". Instantly, she reversed time to the point where destruction never happened and flew into space. Xavier then became determined to change the world.
Meanwhile, Phoenix was traveling through space, meeting with the Silver Surfer, who informed her that wars were being waged in her name and races were committing suicide in her honor. But Phoenix refused to be stopped and went beyond a place the Surfer was guarding to find what she described as heaven.
Banshee
Soon, Jean returned to the Mansion unexpectedly, but she reintegrated with her teammates, even playing baseball. However, even she couldn't defeat the Alpha Flight. She then decided to search Colossus' mind to find out what was troubling him. She soon found out that he was addicted to Banshee to give him super strength. Peter had found out, attacked her and, as a result, because of the school's "zero tolerance, drug-free" rules, she expelled him.
Jean and Xavier soon began testing all students in the Institute for Banshee. They found one positive -- Wolverine. At first mention of the news, he took out his anger on a number of Danger Room robots. He later discovered that the drug was derived from his DNA, making it seem like he had been using it.
Jean soon intensified Danger Room practices, telling the X-Men to push harder at least six hours a day. Kurt Wagner soon communicated with her, asking for help from the side-effects of Banshee. In her astral form, she witnessed Colossus' X-Men fight Acolytes for Banshee. She led Xavier's X-Men to the Urst-ordansky Collective in Siberia to stop Colossus. When she plead everyone to stop, she was interrupted by what seemed like her father. He plead her to move on with her life and to stop pushing her teammates. She recovered Northstar, who was crippled from the waist down, reducing aggression. Everyone but Scott returned home, so Jean followed him into space, where he was staring down at Earth, feeling omnipotent. Jean reminded him he was needed, provoking him into attacking her. The effects of Banshee started to wear off and he would've succumbed to the vacuum if Jean hadn't encompassed him in her fire.
Ultimatum
Jean discovered that Nightcrawler, Dazzler, and Beast had died. Scott, Jean, and Logan went as the "Original X-Men" to stop Magneto once and for all. The remaining X-Men along with the Fantastic Four, Ultimates and SHIELD assaulted Magneto's base, during which they lost several more members including Wolverine, who had his adamantium ripped from his bones by Magneto. In the end Magneto was defeated when Jean downloaded Nick Fury's memories into Magneto, which revealed that mutants were not the next stage of human evolution, but rather a super-soldier experiment gone wrong. Horrified by the truth, Magneto surrendered, and Cyclops executed him with his optic blast
Soon after, Jean was in Washington, D.C. with the remaining X-Men where Cyclops made a speech, attempting to bring a peace to the anti-mutant hostilities and to ask that all mutants surrender to the government. He was then assassinated by Quicksilver, who lodged a bullet into his skull. Scott died in the arms of Storm and Colossus, while Rogue rushed a distraught Jean to safety. Later, Jean, Rogue, and Iceman tore down the Xavier Institute and everything on the estate. Just before burying the many mutant victims of the Ultimatum, Jean Grey revealed that she was no longer connected to the Phoenix and no longer able to manipulate space and time. The only explanation she gave was that she has "been punished", has "wasted it", is "selfish" and "unworthy". They then buried the bodies of the various deceased X-Men on the estate's remains.
Post-Ultimatum
Jean Grey left her life as a superhero and took the alias Karen Grant to live in hiding, using her telepathy to convince those around her that she had been living in Baltimore for three years rather than just a few months, while remaining haunted by those she had lost. Her boyfriend put her picture on Facebook, allowing Mystique and Sabretooth to find out where she was. Sabretooth killed her boyfriend, and Karen then threw him into a bus and dropped two vehicles on him causing them to explode. Later that night, Karen went home to find Wolverine's son, Jimmy Hudson, waiting. She then proceeded to tag along om Jimmy's mission in recruiting mutants to a yet-to-be-known-cause (probably something to do with Quicksilver's Brotherhood). They then recruited Derek Morgan to their cause and proceeded to locate Liz Allan.
Aiding S.H.I.E.L.D.[h]
Jean and her Ultimate X were later seen en route to the SEAR to back up Hawkeye.
After talking with Nick Fury and Valerie Cooper, she returned to Tian, now working for Xorn and returning to her Jean Grey Identity.
[h]World War X
At some point, Jean took over leadership of Tian and infiltrated Utopia. There she assisted them during their conflict with the government, with full intentions of assimilating the Utopians into Tian, but her identity was found out and she began to wage war with Utopia by poisoning the Sentient Seed, attacking them with Robotic Fliers, smearing Kitty Pryde as a terrorist and mentally controlling Jimmy Hudson into attacking her city so she would have a justified reason for attacking Utopia once Kitty stepped down from her leadership.
Kitty attempted one last time to reason with Jean, but this quickly turned into a brawl. Unbeknownst to Jean, Pixie began teleporting people out of Tian, emptying the floating city so that the Utopians could destroy it without any casualties. With the city crashing down around her, Jean was also rescued by Pixie. he was allowed to stay in Utopia, but with her telepathy under check.
Cataclysm
Jean accompanied Kitty when she agreed to help S.H.I.E.L.D. stop Galactus. Jean used her telepathy to attempt to read Galactus' mind, but was soon discovered, prompting Galactus to attack them directly. Jean survived however.
