The "Dark Phoenix Saga" is a storyline from the X-Men comic book series, originally published in 1980. It centers around Jean Grey, a powerful mutant who becomes the host for the Phoenix Force, a cosmic entity that amplifies her abilities. As she gains immense power, Jean struggles with her identity and the consequences of her newfound strength. As the saga unfolds, Jean's transformation into the Dark Phoenix leads to catastrophic events, including the destruction of a planet and the loss of innocent lives. The X-Men, her teammates, must confront the threat she poses, ultimately leading to a tragic confrontation that tests their bonds and moral choices.