WARNING; The following article contains major spoilers for Dark Phoenix, in theaters now.
Fox remained coy about Jessica Chastain's role in Dark Phoenix, and the two-time Oscar nominee was little help, saying she wasn't even playing a character from comic book source material. Ultimately, however, she's doesn't portray Empress Lilandra, as the earliest fan theories proposed, but rather Vuk, leader of the D'bari, a shape-shifting alien race that seeks to harness the power of the Phoenix Force to recreate its home world, which was devoured in an earlier encounter with the cosmic entity.
That revelation is, needless to say, underwhelming when compared to some of the more exciting and thought-provoking speculation that emerged in the months leading up to the film's release.
Theories about Chastain's mysterious character buoyed some of the film's earlier marketing. It helped that the studio offered no clues, with even writer/director Simon Kinberg remaining hush on the subject. Given that the final chapter in Fox's X-Men series is a retelling of the seminal "Dark Phoenix Saga," it was only logical that the thoughts of many fans went first to Empress Lilandra of the alien Shi'ar. After all, they played a key role in the source material, demanding the death of Jean Grey after her consumption of a star resulted in the obliteration of a nearby planet (inhabited by the D'Bari).
Lilandra was sympathetic to Jean's "possession" by the Phoenix Force, and her inclusion in the film would have been organic. Even if Kinberg had subverted the lore and made Lilandra evil, corrupting her so she could use the Phoenix to rebuild a shattered empire, it would have fit into the Shi'ar desire to establish galactic dominance. Instead, Vuk is merely manipulating Jean to eliminate humanity in such a wooden, lifeless manner, so the Phoenix Force can use its spark of creation and remake the D'bari on Earth.
While there are parallels between Vuk and the Shi'ar empress, Lilandra has a lot more heft, because she's much more popular in comics and X-Men cartoons. However, the D'bari are relatively obscure, which is why when shape-shifters were mentioned, absolutely no one thought the "Asparagus people," as they're sometimes called, might be in the running. Instead, theorists believed Fox might introduce its own version of he Skrulls. With Captain Marvel also using those better-known shape-shifting aliens, some fans guessed Chastain could instead play Queen Veranake.
Still others tipped Chastain to play Cassandra Nova, the sadistic twin of Charles Xavier who tried to kill him in the womb. That would have added tension, especially as we know Professor X keeps secrets from his students. An evil sister, still alive and using his most powerful weapon against him, would have been the perfect tool to break apart the X-family. Given Xavier's shady past and his tampering with Jean's mind, seeing her as the Phoenix, manipulated by Cassandra, undoubtedly would have crushed Xavier's mind and spirit.
Cassandra has been a powerful enemy for the X-Men since her introduction in 20o1, and she recently used nanites to attempt to wipe out the young generation of mutants. Such a move would surely have positioned her as a formidable telepath who pushes Xavier and Jean to their limits, maybe even leaving an opening for Cassandra to use the Phoenix Force herself. Sadly, with the disappointing Vuk reveal, and seeing her exploit the Phoenix Force in such boring fashion, the Cassandra theory feels like wasted potential.
Last but not least, another intriguing theory was that this character was actually a manifestation of the Phoenix Force, appearing only to Jean in a manner similar to the villainous Mastermind in the original "Dark Phoenix Saga." That would have provided an avatar for the cosmic entity's sentience, adding character and personality to an abstract being.
Ultimately, however, all of those theories were nothing more than wishful thinking.
Directed and written by Simon Kinberg, Dark Phoenix stars James McAvoy, Michael Fassbender, Jennifer Lawrence, Nicholas Hoult, Sophie Turner, Tye Sheridan, Alexandra Shipp, Kodi Smit-McPhee, Evan Peters and Jessica Chastain.