Jean Grey was born the youngest of two daughters to John and Elaine Grey. She had a normal life, born and raised in New York. A traumatic incident occured while playing with her friend Annie Richardson. Annie was hit by a car and the emotional stress of the accident caused Jean's mutant powers to manifest well before she reached even pre-pubescence.
On a mission back from space, entering the top layer of Earth's atmosphere, Jean's psionic shields became overwhelmed and the radiation began to eat away at her body, slowly killing her. With her last ounce of strength, she telepathically cried out for help and was heard by the Phoenix Force.
The Phoenix offered to save Jean, but told her that she would need time to heal because her body was already far more damaged than her mind would allow her to realize.
Jean accepted the entity's help and the Phoenix siphoned a small piece of her essence and created a copy of Jean’s body for itself.
Jean is one of the strongest comic book characters. Her powers include: Psionic force, telepathy, telekinesis, matter manipulation, and flight. Her abilities were magnified to astonishing levels when she was infused with the Phoenix Force.
"Hear me, X-Men! No longer am I the woman you knew! I am fire! And life incarnate! Now and forever -- I am Phoenix! "