The Dark Phoenix Saga is one of the most beloved X-Men storylines of all time. The classic arc has the good-natured telepath Jean Grey dealing with the all-powerful Phoenix Force that has seemingly inhabited her body. After Hellfire Club shenanigans lead the Phoenix to become corrupted, Jean Grey ultimately chooses to sacrifice herself for the greater good. The epic tale, by Chris Claremont and John Byrne, features themes of love and loyalty tested as well as ultimate corruption and redemption. Unfortunately, what came after The Dark Phoenix Saga was endlessly convoluted.
The Phoenix first appeared in Uncanny X-Men #101 in 1976. An immortal cosmic being, the Phoenix first encountered Jean Grey during an X-Men mission in outer space. After becoming Phoenix, Jean Grey received a significant boost in her abilities, which now included cosmic awareness and the ability to manipulate life force, in addition to telepathy and telekinesis. This led the mutant Mastermind to begin seducing Phoenix with the hope of bringing her into the fold of the Hellfire Club. They almost succeeded - with Jean becoming their Black Queen - but Phoenix broke free from their mental conditioning, becoming the Dark Phoenix instead. Fully corrupted, the Dark Phoenix eventually destroyed an entire star system - with a population of over five billion - prompting the alien Shi'ar to demand her execution. The X-Men came to her defense, but Jean was able to trigger a nearby cannon and vaporize herself, taking the Phoenix down with her.
The events of The Dark Phoenix Saga were shocking at the time, as it showed the beloved X-Man Jean sacrifice herself in order to save the lives of both her love Cyclops as well as her friends. It's one of the most memorable endings in all of comics, but unfortunately, it's not the final ending for the Phoenix... or Jean Grey. The Avengers and Fantastic Four would later find Jean Grey, alive and well, in a cacoon in Jamaica Bay. The Dark Phoenix Saga was retconned to reveal that Phoenix was only a duplicate of Jean Grey, and the genuine article was alive and well the whole time.
The Phoenix Force would seek out Jean again, who would reject it after its galaxy-consuming actions. It would instead find its way to Jean's deranged clone Madelyne Pryor, aka the Goblin Queen, before eventually returning to Jean Grey. Beyond this, Rachel Summers, the daughter of Scott and Jean from an alternate future, also held the Phoenix Force for a long time before a confrontation with Galactus drove it away, though Rachel still retains a small portion of its abilities.
Jean Grey would later perish - for real - during a confrontation with Magneto sometime later. The Phoenix Force - and Jean Grey herself - drifted in and out of focus over the next few years. It would not be until the Avengers vs. The X-Men storyline that the Phoenix would play a major role, this time bonding with five rogue X-Men - Cyclops, Emma Frost, Namor, Colossus, and Magik. Over the course of the conflict, Cyclops would become the Dark Phoenix, killing his mentor Professor X. Later, the reconstituted Phoenix Force would resurrect Jean Grey again, only to be rejected a final time. However, this comes with the most recent development, with Namor now hoping to reclaim the Phoenix for himself in his ongoing feud with the Avengers.
While the revolving door of life and death is nothing new in comics, it ultimately does a disservice to The Dark Phoenix Saga. The retcon undermines Jean's actions near the end of the story arc since it was ultimately revealed to be the actions of her duplicate, not Jean Grey herself. Still, the convoluted post-Dark Phoenix saga has led to some high points, such as Phoenix appearing as a member of the Avengers One Million B.C., as well in the five-way Phoenix battle in Avengers vs. X-Men. However, it's tough for any of these stories to top the epic conclusion of the original Dark Phoenix tale, written nearly forty-five years earlier.