So buckle up for a look at Jean's wildly complicated history and how it relates to the Phoenix Force before Sophie Turner returns to the role in 2019 finale for the current series of X-Men movies.
Jean was one of the original five X-Men, a team of mutant heroes led by Professor Xavier that included Cyclops, Beast, Angel and Iceman (she went by the lame code name Marvel Girl).
Years after the character first appeared in 1963's The X-Men No. 1 -- by writer Stan Lee and artist Jack Kirby -- we found out Xavier put psychic barriers around her powers because she couldn't control them. She even touched the mind of the young Scott Summers while in the form of a burning Phoenix. Summers would eventually become Cyclops, and Grey's frequent off-and-on-again love interest.
Judging by the trailer, it looks like Xavier's ethically questionable act (one of many he's committed through the years) will be mirrored in the Dark Phoenix movie.
From the ashes
Returning from a mission to space in 1976's Uncanny X-Men No. 101 (by legendary writer Chris Claremont and artist Dave Cockrum), Jean is exposed to a lethal dose of radiation and the team's shuttle crash-lands in New York's Jamaica Bay. Scott and the rest of the X-Men manage to get out, but Jean is nowhere to be seen.
Instead of dying, she bursts from the waters and takes the code name Phoenix, which is a whole lot cooler than Marvel Girl.
This leads to the main event, the Dark Phoenix Saga, which ran from Uncanny X-Men No. 129-138 (by Claremont and writer/artist John Byrne)
Jean's wildly boosted powers bring her to the attention of the villainous Hellfire Club, whose members fancied themselves Marvel's Illuminati long before the heroes did. They got the telepathic Mastermind to manipulate Jean into unleashing her full potential.
This drives Jean totally over the edge, and she renames herself as the even cooler "Dark Phoenix" before she flies through the universe and makes a star go supernova, wiping out the 5 billion beings on a nearby planet. That's considerably less cool, but it certainly upped the stakes.
As a bunch of alien races call for Jean's head, Professor Xavier places psychic barriers in Jean's mind and reduces her powers to her pre-phoenix level, bringing her normal personality back.
When the X-Men learn that the alien races plan to wipe out Earth's solar system to ensure Dark Phoenix is really gone, Jean takes her own life (using an ancient weapon of the Kree, who recently had a big MCU moment) to save Scott and everyone else.
Absolution and Return
After Jean's apparent death, Scott falls in love with Madelyne Pryor, a woman who's physically identical to Jean (because comics are just strange sometimes). She's later revealed to be a clone of Jean created by X-villain Mister Sinister, who's obsessed with mixing the Summers/Grey genes to create the ultimate psychic mutant.
The Avengers later find Jean in a cocoon deep in Jamaica Bay in Fantastic Four No. 286, by Claremont and Byrne. We learn that the Jean who became Dark Phoenix was a duplicate created by the Phoenix Force, an all-powerful cosmic entity.
Scott abandons Madelyne and their son Nathan to return to Jean. Does this make him a total jerk? It's hard to imagine oneself in that situation, but it just doesn't seem OK. Madelyne doesn't think either, as evidenced by her demonic turn.
Establishing Jean as a separate being from the Phoenix was Marvel's slightly ham-fisted way of absolving her of her genocidal act during the Dark Phoenix Saga, but it served its purpose in getting her back in action.
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Jean and the Phoenix were later established as a single being, with the revelation that she was the Phoenix's host body. She was killed again by Magneto after he pretended to be a mutant named Xorn (that's a whole different rabbit hole) in 2004's New X-Men No. 150 by writer Grant Morrison and artist Phil Jimenez.
This time, Jean stayed dead for 13 years … aside from her younger self being plucked from her timeline and brought to the present in 2012's All-New X-Men No. 1 (by writer Brian Michael Bendis and artist Stuart Immonen).
The adult Jean only just returned in 2017, in the five-part Phoenix Resurrection miniseries (from writer Matthew Rosenberg and artist Leinil Francis Yu)
It's pretty trippy, as we learn that the Phoenix Force has kept Jean in a psychic construct of her childhood neighborhood, with no memory of her life as hero, as it tries to make her its host once again. She breaks free and rejects the Phoenix once again, returning to her teammates.
She led her own team in the ongoing X-Men Red series written by Tom Taylor and illustrated by Mahmud A. Asrar… but we'll see how long Jean can go without the Phoenix making another return.
X-Men: The Last Stand
You might remember the previous attempt to have Jean go Dark Phoenix in a movie. The character was played by Famke Janssen in the first few X-Men movies, and she was seemingly killed saving her teammates in 2003's X-Men 2. The movie's final image hinted that she'd return as the Phoenix, much to everyone's excitement.
Then X-Men: The Last Stand happened. This messy movie used elements of the classic comic book storyline, but didn't give it enough time to develop and reduced Jean's dark side to little more than a henchwoman to Magneto.
At the end of the movie, Jean's true self surfaces and she begs Wolverine -- who basically had to do everything in the first few movies because Hugh Jackman is amazing -- to kill her. It should've been an emotional sacrifice, but it felt empty after such an overstuffed narrative.
Bryan Singer directed the first two movies but left the third to do Superman Returns, leaving the chair open for Brett Ratner. Singer screenwriter Simon Kinberg clearly weren't happy with how Ratner's movie left things, so they wrote The Last Stand out of the timeline with time travel antics when Singer returned to the franchise in 2014's X-Men: Days of Future Past.
A younger Jean (Sophie Turner's first time playing the role) made her debut in 2016's X-Men: Apocalypse, which is set in 1983. In the final battle of that movie, James McAvoy's Xavier tells Jean unleash her full power to kill the titular villain… what could go wrong?