Jyn Erso is a fictional female in the Star Wars series. The character was portrayed on screen by Felicity Jones. Her allegiance / loyalty is to the Rebel Alliance. Jyn Erso is the lead protagonist in the Star Wars - Rogue One, a spin-off of the main Star Wars film storyline. Jyn is the only female in the group of rebels that is tasked with the theft of the plans. Jyn is described as a forger, a thief and having possession of stolen Imperial documents, just the kind of person you need if you're going to steal plans of the Imperial Death Star. Jyn's character only appeared in the one film. There has been speculation and rumours on the internet that she is the mother of Rey but there were no hints either way to substantiate or reject the rumours.
Jyn Erso was born to Galen Erso and his wife Lyra. The Erso family hid out on Lah'mu, a remote planet away in the hope that they would not be discovered by the Galactic Empire. The planet was a rocky planet like Earth which had Jupiter like rings. They lived without all the mod-cons, living a simple farming life. At the start of the film, Jyn Erso is only a child.
Before living on Lah'mu, Galen Erso had worked for the Galactic Empire on their weapons systems. Galen had become conflicted with working for the Empire and had sought to leave the organisation. In the film, you see memories of Galen with other Imperial employees discussing their work before he comes over and sees Jyn in one of her happy memories.
When Director Krennic finally discovered where Galen was, Krennic paid Galen a visit. Krennic wanted all three members of the family, Galen, Jyn and Lyra to come back with him so Galen could work on the Empire's secret weapon, the Death Star . After making sure that Jyn was going to be safe, Lyra confronted Director Krennic and his black Stormtroopers. It didn't end well and Jyn witnessed her mother being killed after Lyra got a shot off on Director Kreenic. Jyn went and hid down a shaft until she was discovered by Saw Gerrera who cared for Jyn until Jyn was a teenager and then deserted her.
Not much is then known after Jyn was deserted by Saw until the moment we see her being held in an Imperial prison and then subsequently being rescued by a Rebel Alliance group from a land based prison transporter. It is not explained in the film why Jyn Erso has ended up on the planet of Wobani. All we know is that she's using an alias and that the Galactic Empire are unaware of her real identity. Had the Galactic Empire known, Jyn wouldn't be on the planet but instead reunited with her father. The first member of the Rebels that Jyn Encounter is K-2SO who congratulates Jyn on being rescued.
Jyn was taken to the Rebel Alliance based on a moon of Yavin IV where she was given a mission by Mon Mothma. Mon Mothma wants Jyn Erso to find Saw Gerrara and try and persuade him to come back into the fold and to stop the attacks on the Imperials that could harm the Rebels standing. Saw Gerrara had become an extremist and was loosing sympathy. It is in the Rebel base that Jyn meets her mission partner, Cassian Andor for the first time where they are introduced to one another by Mon Mothma.
Cassian and Jyn went to the planet of Jedha, a desert planet and to the largest inhabited city on the planet which was also not far from Saw Gerrara's hideout. After a skirmish between rebels and the Galactic Empire in the city, both Jyn Erso and Cassian Andor are taken prisoner and taken before Saw Gerrara. Jyn wants to confront Saw for leaving her behind but is not happy with the response. When Grand Moff Tarkins decides to test the laser on the city, the surrounding area is completely destroyed. Jyn and Cassian Andor escape with some new recruits to the Rebels including that of Bodhi, an Imperial Pilot who has defected.
From Jedha, Jyn with the rest of the team visits the rainy mountainous planet of Eadu where unbeknown to her, her father is currently at the base working for the Galactic Empire.
Jyn wanted to see her father once more but she never got the chance. Galen was killed during a strike by X-wings. Cassian Andor was going to assassinate her father but at the last moment, he didn't fire the shot. Jyn saw her father's lifeless body and tried to get close but Cassian was there to hold her back and get her to safety.
When Jyn returned to the Rebel base on Yavin IV, she wanted to lead a team to Scarif and steal the plans for the Death Star. The Rebel Alliance leadership rejected her request for a group. A small group of Rebels decided to join her because she was determined to go with or without the Rebel Alliance leadership's consent. One of those who agreed to go with her is Cassian Andor.
The plans for the Death Star are stored in the Galactic Empire computers on the tropical planet of Scarif. The team led by Jyn Erso and Cassian Andor steal the impounded Imperial cargo ship from the Rebel Alliance which in turn had been stolen from the Empire earlier. Bodhi Rook makes up their call sign as Rogue One. They make it to the planet where they manage to sneak into the base using stolen Imperial clothing, Jyn Erso, Cassian Andor and K-2SO sneak into the data storage building whilst the others Baze and Chirrut fight the Empire outside the base.
Jyn Erso and Cassian Andor make it to the data storage area and manage to locate where the plans are being held. The computer hard disk is labelled Stardust after Galen's affectionate name for his daughter. Cassian is knocked out and it looks like Jyn is on her own as she makes her way to the top of the base to transmit the plans. At the top, Director Krennic appears but he is unable to stop the uploading of the plans. Before Krennic shots Jyn, he is shot by Cassian who has woken up.
The Death Star under the control of Grand Moff Tarkin arrives and fires a shot at the Scarif base. Neither Cassian nor Jyn Erso is able to get off the planet in time before the Death Star death ray hits the planet. The two die in one another's arms as the flames engulf the planet.
The relationship between Jyn Erso and Cassian Andor is all too brief. The relationship doesn't have enough time to mature into a full blown relationship like that of Han Solo and Princess Leia. However if their characters had lived long enough, its pretty guaranteed that these two would have gone the distance. Although there is speculation that Jyn is Rey's mother. There is no speculation on the internet that Cassian is Rey's father.