Ros
A shrewd, ambitious redheaded woman from near Winterfell who works her way from a northern brothel into the trade and intrigues of King's Landing.
A soul born at The North.
The fuller tale
Season One
A prostitute at the brothel outside Winterfell where Theon Greyjoy is a regular customer and a worse tipper than his rank would suggest, one of the first people in the story to see exactly what Theon is when nobody important is watching. She turns up again in King's Landing working for Littlefinger, whose brothels function as half information exchange and half business, and who values a clever, observant woman for reasons that go well beyond the obvious ones.
Season Two
Employed by Littlefinger and quietly informing on him to Varys at the same time, playing a game considerably more dangerous than the one either man thinks he's running. She helps get Shae settled into Sansa's household as a favor that costs her nothing and buys her some safety, or so it seems. When Joffrey takes his temper out on two of Littlefinger's girls with a crossbow for entertainment, Ros is one of them, and survives it with the kind of fear that doesn't go away just because the king moves on to something else.
Season Three
Littlefinger works out, or decides it no longer matters whether he can prove, that she has been carrying his business to Varys, and rather than simply killing her himself he finds a use for the betrayal — handing her over to Joffrey as a gift. The king, who has never needed much of an excuse, kills her with a crossbow the way he tortured her with one the year before, and Littlefinger lets her body be found where Varys will hear about it, a message about what happens to people who work both sides of his table.
How it ends for them
On the screen. Killed in the Red Keep (S3·E6)
The clever girl from the Winterfell brothel rose all the way into Littlefinger's confidence, and Varys's. When Baelish found the leak he gave her to Joffrey, who ended her with a crossbow in the Red Keep.
She dies for the leak. When her warnings to Varys about Sansa Stark cross Littlefinger's plans once too often, Baelish audits his own house, identifies the informer, and — in his velvet way, narrating his philosophy of useful failures to an unrelated audience — writes her off as a bad investment. He gives her to Joffrey. The show reveals the transaction after the fact, in a single image without dialogue: Ros in the king's chambers, bound to the bedpost, dead of a crossbow with the bolts placed at the young king's leisure — Joffrey lounging opposite with the weapon, a boy finished with a new toy. It is among the show's coldest cuts precisely because no scene of it exists: her death is shown as Littlefinger describes disposal, a line item. Being show-only, she has no book fate — the women who share her duties on the page, Alayaya among them, survive their punishments.
Their chapters, book by book
Where the page and the screen part
No Ros exists in the novels; she is a composite the show built to give faces and continuity to the books' scattered brothel scenes. Her narrative duties are performed on the page by several women — Chataya and her daughter Alayaya in King's Landing, whose establishment shelters Tyrion's secrets and who suffer for their proximity to him; the unnamed Winterfell girls of Theon's chapters; and the anonymous informants any spymaster keeps among the pillows. Alayaya in particular absorbs the books' version of her jeopardy: seized and threatened by Cersei as leverage against Tyrion, whipped on Joffrey's order, but alive. The show found it could not keep hiring new actresses for one function, consolidated the role, and — having made her a person — made her fate one of its early statements that television inventions enjoyed no plot armor.