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Vuk: The X-Men fear you. And what they don’t understand, they fear. And what they fear… Jean Grey: They seek to destroy.
~ Vuk influencing Jean Grey against the X-Men.
Are you scared, little girl, who answers to a man in a chair? Or are you the most powerful creature on the planet?
~ Vuk to Jean Grey about Charles Xavier - her most famous quote.
Vuk, under the identity of Margaret Smith, is the main antagonist of the 2019 superhero film X-Men: Dark Phoenix, the final installment of the X-Men film series. She is the leader of the D'Bari, a race of extraterrestrials who were near-extincted when the Phoenix Force absorbs their sun, who comes to possess Jean Grey and works to manipulate her to transform the Earth in a new world for the D'Bari race.
Vuk started out as a member of the D'Bari, before rising herself up as a supreme leader of their home planet. However, it wasn't until a unimaginable destructive cosmic entity (known as the Phoenix) wandered across the universe, and later used its powers to destroy the D'Bari's planet, leaving only Vuk and many few D'Bari as survivors. Because of this event, Vuk vowed to get revenge on the Phoenix and find a new home planet for her race.
In 1992, Vuk and her posse traveled to Earth, where they used their shape-shifting abilities to take on human disguises; even Vuk takes the form of a young tall and white-haired woman named Margaret Smith that she briefly killed. She soon learns that the young mutant Jean Grey absorbed the Phoenix into herself after the X-Men's previous mission to save several astronauts and it also caused her to accidentally killed the mutant Mystique and several police officers. Out of fear, Jean heads over to the island of Genosha for safety (inhabited by mutant refugees led by Magneto), but is turn down by Magneto after she tried to kill several arriving soldiers tasked for her arrest. Seeing that Jean has no one left to turn to, Vuk meets her in person and tells her about the history of the Phoenix, convincing her to use her powers for her own use.
When Magneto and the mutant refugees conspired to kill Jean in New York City for what she did, Professor Xavier and the X-Men arrive to stop them. Magneto was able to make his way to confront Jean, but thanks to Vuk's guidance, Jean was able to overpower him. However, Xavier uses his mind-reading abilities to let Jean read his thoughts about why he repressed her memories, which drove her into asking Vuk in taking away the powers. Vuk eagerly does so, but not before she tells Jean that doing so will also deprive Jean of her life, as Vuk intends to use the Phoenix power to destroy all life on Earth so that she can create a new haven for the D'Bari race there. Fortunately, Xavier and Scott manage to stop Vuk from draining most the Phoenix power, but several soldiers (sent by the U.S. government) arrive to arrest all the mutants (including Xavier, Magneto and Jean).
With all the captive mutants boarding on a train to a mutant containment facility, Vuk (being on the end of her wits) lead her D-Bari soldiers to attack the train, overpowering the soldiers. This forced the surviving soldiers to release the mutants and let them battle against the D-Bari soldiers. Though most of the D'Bari soldiers are finished off, Vuk manages to use her powers (fueled by some of the Phoenix power that she absorbed) to defeat all the mutants (including Xavier and Magneto). However, Xavier helps Jean in gaining control of her Phoenix power, allowing herself to finish off the remaining D'Bari soldiers. Jean then takes Vuk into outer space, where she uses the Phoenix power to disintegrate Vuk to her death for good.