Dark Phoenix

A woman with red hair wearing a red, orange, and gold costume appears to be hovering in the air, over a white/tan background. 

Created in 1980, the Dark Phoenix is the overly powerful and essentially evil version of X-Men superhero Jean Grey. The character first appeared in the “Dark Phoenix Saga,” a popular and beloved arc in Uncanny X-Men’s run.

During a mission in space, Jean exposes herself to a deadly solar flare to save the rest of the X-Men. This sacrifice results in her death and eventual rebirth as the Phoenix, a significantly more powerful version of herself. When a villain called Mastermind tries to manipulate and control Phoenix, it backfires, and results in the awakening of the Dark Phoenix, turning Jean into a nearly unstoppable supervillain. While the X-Men and others try to subdue her, the only person able to stop Jean is herself. In another sacrificial act, Jeans ends her own life, knowing her power would eventually consume her and those she loved. 

During her time as Dark Phoenix, Jean killed billions, making it difficult for Marvel to resurrect the character as one of the heroes of the team. The writers chose to rectify this issue by writing a story that revealed that Jean was actually overtaken by an entirely different entity named Phoenix when she committed these atrocities, ridding her of all guilt.