From Cassius Comics

A being of sentient energy and indestructible power, the Phoenix Force is one of the most powerful entites in the universe. It first became known in the Sol system when it secretly took the place of the X-Man known as Jean Grey. Placing Grey in a stasis cocoon, the Phoenix Force came to believe that it was in fact Grey itself; however, the entity was unprepared for some of the more negative emotions that a human can experience, and mental tampering by Mastermind inadvertently transformed it into the Dark Phoenix. In this new, uncontrollable form, the force consumed the energy of a star, destroying an entire populated solar system and drawing the attention of the Shi-Ar. The Phoenix Force was returned to a rational state by the X-Men, but it and the team where immediately abducted by the Shi-Ar, who demanded the Phoenix's death (as all parties involved still thought that it was Grey). The Phoenix Force and the X-Men battled the Shi'Ar Imperial Guard for the creature's right to live, but feeling itself reverting to its Dark Phoenix state, the Jean Grey-formed Phoenix Force committed suicide. Grey was thought to be dead by all parties, and the Phoenix Force presumably remembered its true place in the universe. Grey was eventually discovered and returned to her previous life.

Although it rarely again manifested as its own form, the Phoenix Force has empowered a number of women, including Rachel Summers, the Goblin Queen and Grey herself later in life. In all of its forms the Phoenix has manifested as the form of a gigantic bird of flames. It has enhanced all of the women's latent telepathic and telekinetic abilities, in Grey's case reaching levels of near-omnipotence. While serving as the last vessel for the Phoenix Force, Grey was killed by Xorn, while he was impersonating Magneto. Although she could transcend death as easily as her namesake, Grey chose to remain dead in order to prevent a resulting horrific future (referred to as "Here Comes Tomorrow"). Following her death, the Phoenix Force did manifest as itself one last time, searching for a new potential vessel in either Quentin Quire or Emma Frost, but neither of its attempts proved fruitful.