Alys Karstark

"Now and always."

- Alys renews House Karstark's pledge of fealty to House Stark

Lady Alys Karstark is the daughter of Lord Harald Karstark and the new head of House Karstark after the death of her father at the Battle of the Bastards, who fought for House Bolton. She pledges her house to House Stark once again when called upon by Jon Snow.

Background
Alys Karstark is the daughter of Harald Karstark and granddaughter of Rickard Karstark. As House Karstark is a younger cadet branch of House Stark, Alys Karstark is a distant cousin of the main Stark family.

During the course of the War of the Five Kings, Lord Rickard's other two sons Torrhen and Harrion Karstark were killed. Jaime Lannister personally killed Torrhen, leaving Rickard outraged when Catelyn Stark freed him for a prisoner exchange. Denied his vengeance as a father, Lord Rickard and his men killed two minor Lannister cousins who the Starks had also taken prisoner. King Robb Stark was disgusted that Lord Rickard would kill two unarmed and captive boys, and without his permission. Declaring it to be murder and treason, Robb sentenced Lord Rickard to death and (as per Northern custom) personally executed Lord Rickard by beheading him with his own sword. This caused the Karstark contingent in the Northern army to abandon the war and return home. House Bolton later betrayed the Starks at the Red Wedding, slaughtering their army and killing King Robb.

As his father's last surviving son, Harald Karstark became the new head of the House. When Ned Stark's bastard son Jon Snow and Sansa Stark tried to rally the North against the Boltons, Harald was still embittered by Robb's execution of his father, so he sided against the Starks. Harald joined the Karstark army with Ramsay Bolton's main force and engaged the smaller Stark loyalist army at the Battle of the Bastards. At the last minute, a massive new army from The Vale of Arryn arrived: the Bolton forces were pinned between them and the remaining Stark army and were totally destroyed.

Lord Harald died at some point in the battle, leaving his daughter Alys Karstark as the new heir to House Karstark.

Season 7
Alys is present at a council of Northern and Vale lords in Winterfell's main hall presided over by the King in the North, Jon Snow. The council discussing how to deal with the coming threat of the White Walkers, and how to deal with the fallout of the defeat of the Boltons. Sansa Stark, Snow's half-sister and advisor, suggests giving Karhold to one of the Northern lords who had been a proven ally of the Starks, but Jon dismisses this idea, as Alys wasn't to blame for Harald Karstark's actions. The argument of what to do with the surviving Karstark and Umber children goes back and forth. Ultimately, Jon calls Alys and Ned Umber forward. They are visibly afraid that Jon will announce that he will execute them. Instead, Jon holds to his original position that he will not hold them responsible for the crimes of their fathers, and orders them to swear fealty to the Starks once again. Relieved, without hesitation Alys and Ned ceremonially kneel, draw their swords, and swear to serve Jon and the Starks. This allows Alys to retain her inheritance as the new Lady of Karhold.

Alys is also present when Jon announces his plans to leave for Dragonstone, to make an alliance with Daenerys Targaryen in order to defeat the Night King, and leave Sansa in control of the North.

In the books
In the A Song of Ice and Fire novels, Alys Karstark is the only daughter of Lord Rickard Karstark, Lord of Karhold, and appears much earlier in the narrative than in the TV series, before Stannis Baratheon's death and while Jon Snow is in the Night's Watch. She is described as tall and skinny, with brown hair and a long face (somewhat similar to Arya). As the Karstarks are a cadet branch of House Stark (that split off a thousand years ago) she is also a distant kinsman of the main Stark line - so her resemblance to Arya isn't coincidental. She is the sister of Torrhen Karstark, Harrion Karstark, and Eddard Karstark (renamed "Harald" in the television series). In the books, Alys is actually two years older than Sansa Stark, and around one year younger than Robb Stark and Jon Snow.

Alys is a headstrong girl who knew Robb Stark and Jon Snow during childhood. Her father hoped to have her betrothed to Robb to strengthen ties with the Starks, though nothing came of it. She danced with both of them at feasts, finding Robb courteous but Jon somewhat sullen. Jon vaguely remembers that, since Alys was six years old at the time (and Jon was around seven or eight years old).

She was later betrothed to Daryn Hornwood, heir of House Hornwood, until he was killed in the Battle of the Whispering Wood. After Ser Jaime Lannister was released by Catelyn Stark, Lord Rickard promised Alys's hand to whoever brought the Kingslayer to him, in order to avenge the deaths of his sons Eddard and Torrhen, who were also killed by Jaime. Alys's surviving brother Harrion is taken captive at the Battle of Duskendale. He was imprisoned in Maidenpool, but it has been almost a year since his surviving kin received news about it, and it is uncertain if he is still alive.

Following Rickard's death, his treacherous uncle Arnolf, who secretly collaborates with the Boltons, schemes to take over Karhold: he announces in public that he supports Stannis (intending to stab him in the back while fighting the Boltons), hoping that the Lannisters will execute Harrion as a punishment, then Alys will become the heiress of Karhold. Arnolf plans to force Alys to marry his son Cregan (though he is her first cousin once removed, this is not considered incest in Westeros). They also plan to dispose of her as soon as she gives birth to a son by Cregan, who has already buried two wives.

Alys finds out about Arnolf's twofold treachery, escapes to Castle Black and informs Jon what her great-uncle is up to. She has no idea what became of her brother Harrion as a result of Arnolf's fake announcement.

Alys resents Robb Stark for killing her father. Though she knows for what crime her father was executed, it does not make a difference for her, but since Jon belongs to the Night's Watch, there is no blood feud between them, and she asks his help to save both her and Stannis from Arnolf. Jon quickly sends Tycho Nestoris to find Stannis and warns him of the traitor in his host, and he does. Arnolf, his son Arthor and grandsons are arrested, and Stannis intends to execute them: if they admit their guilt - they will be given the same swift death Robb gave Rickard; if not - they will be burned alive.

The battle of Winterfell has not come yet to a conclusion by the point the novels reached (it has not even begun), but thanks to Alys the Boltons have been denied of one of the advantages they had over Stannis.

Meanwhile, to keep the Boltons and Arnolf from forcing Alys into a marriage to seize her birthright, Jon quickly arranges for Alys to marry Sigorn, the son of Styr and the new Magnar of the Thenns who has become one of his allies, to found House Thenn. Alys complies voluntarily, and when Cregan arrives to reclaim Alys, Jon has him arrested and placed in an ice cell.