Jean Grey was the first female member of the X-Men, a team of mutants assembled by Professor Charles Xavier to defend humanity from itself and from other mutants who might wish to cause it harm. Jean was once host to the cosmic being known as the Phoenix Force, which amplified her powers to an unimaginable level. The Phoenix Force was driven insane, and Jean caused it to commit suicide, saving the universe. It was later revealed that the Phoenix had created a duplicate of Jean's body in order to continue living her life while the real Jean was recovering from the damage inflicted by solar radiation at the bottom of Jamaica Bay. Eventually, the real Jean returned to the X-Men to fight alongside her friends and the love of her life, Scott Summers/Cyclops. She has since retaken the codename Phoenix, though the abilities remaining at her disposal are those she was born with.
Jean was the second daughter born to John and Elaine Grey, after her sister Sara. Jean was raised in Annandale-on-Hudson, New York, where she had a relatively normal childhood. When Jean was ten, her best friend, Annie Richardson, was hit by a moving car. Jean watched in horror as Annie succumbed to her injuries, her own grief multiplied as she felt Annie's emotions leading up to her death. This was caused by Jean's newly-awakened telepathy, which thereafter refused to disappear. Jean found she could read the minds of others, and the overwhelming amount of emotion and information she received with no way to handle them sent her into a deep depression.
When Jean was eleven, her psychiatrist recommended she speak to Professor Charles Xavier. Xavier was a mutant, like Jean, and he offered to teach her to master her abilities. He took her in as his first student, and he helped her to develop her telepathy and the telekinesis that appeared later.
Other students soon arrived at the Xavier Institute for Gifted Youngsters. These included Warren Worthington III/Angel, Hank McCoy/Beast, Bobby Drake/Iceman, and Scott Summers/Cyclops. Jean and Scott immediately developed feelings for one another, though both were too shy to admit this. When they finally did, they became inseparable.
Professor Xavier trained his students to master their abilities and use them for the greater good, fighting the villains who used their powers to endanger the lives of others. The X-Men worked as a team, and its members became very close friends. Eventually, other students came to the school to learn from Professor Xavier and joined the X-Men. One of these was Logan/Wolverine, with whom Jean has always shared a romantic tension, though her heart belongs to Scott.
On a mission to space, Jean and the other X-Men were captured by Stephen Lang and his Sentinels. The X-Men eventually escaped and flew a space shuttle to Earth. During their return trip, a terrible solar radiation storm assaulted the shuttle, killing the pilot. The X-Men needed someone to guide the shuttle safely back to Earth, but the damaged ship would not protect whomever attempted to fly it from the radiation. Jean volunteered, using her abilities to shield herself as she flew the shuttle toward home. Eventually, Jean was unable to save herself from the radiation. She telepathically cried for help, and the cosmic entity known as the Phoenix Force answered. It granted Jean her heart's desire: to save the lives of herself and the X-Men. It placed Jean in suspended animation at the bottom of Jamaica Bay to heal while the Phoenix created a duplicate of her body and took on her persona, joining the X-Men and resuming Jean's relationship with Scott.
Everyone believed the Phoenix to be Jean. Thus, they were heartbroken when the woman who had continued to fight alongside them with her newly-quantified powers was brainwashed by the villain Mastermind and driven mad. She renamed herself Dark Phoenix and became an enemy of the X-Men. Dark Phoenix destroyed a star in the system governed by the Shi'ar, an advanced alien race. The Shi'ar demanded Jean answer for her crimes, and they sentenced her to death. A battle took place on the moon between the Shi'ar the the X-Men, who fought for Jean's life. In the end, Phoenix killed herself in order to save the others.
Eventually, the real Jean was discovered by the Avengers. She returned to the team and to Scott, and after much thought, she took the name Phoenix to honor the entity that had died to protect those she loved. She is currently one of the team's leaders, and she and several others are on a trip to England to investigate suspicious activity reported by Professor Xavier. Jean and Scott flew the Blackbird, and upon their landing, a bomb was detonated, killing Shadowcat and injuring Jean and the rest of the team. Jean managed to shield Scott and herself somewhat, but not enough to keep them from being harmed.