Dark Phoenix

Dark Phoenix is not a person. It is what happens when the Phoenix Force, the cosmic embodiment of life, death and rebirth, bonds to a mortal host and the host's restraints come off. Jean Grey was the vessel, and for a while the arrangement looked like a gift: a telepath elevated to something that could reshape matter and cross galaxies unaided. The Force feeds, though. It always feeds. And because it experiences the universe through a human nervous system, it inherits every appetite, resentment and buried desire that nervous system carries, then amplifies them to a scale where a bad afternoon becomes an extinction event.

Mastermind found the crack. Working for the Hellfire Club, he spent months layering illusions into Jean's mind until she believed herself the Black Queen, and the psychic seduction did what no cosmic villain had managed: it unlocked the Phoenix without conscience. What emerged consumed a star in the D'Bari system for the sheer pleasure of it and killed five billion people who never knew the X-Men existed. The Shi'ar came for judgement, the Imperial Guard fought her on the Blue Area of the Moon, and it ended with Jean choosing a Kree disintegrator beam over the thing wearing her face.

The Dark Phoenix Saga is the story that turned the X-Men into Marvel's flagship, and it nearly ended differently. Claremont and Byrne originally planned to strip Jean of her powers and let her live, but editor-in-chief Jim Shooter insisted that a character who had committed genocide could not simply be depowered and forgiven, so the finale was rewritten and redrawn late in production into the suicide on the Moon. Marvel then spent six years wanting Jean back, and solved it in the pages of Fantastic Four in 1986 by splitting her from the Force entirely, a retcon that launched X-Factor and made the Phoenix a separate character with its own history of hosts, from Rachel Summers to Hope Summers to Quentin Quire.