Ellaria Sand
Oberyn's paramour, a bastard of House Uller and mother to several of his Sand Snakes — in the show, as ready for vengeance as any of them.
The fuller tale
Ellaria Sand is a bastard of House Uller of the Hellholt — in Dorne, the books remind us, sand is a surname and not a sentence — and the great love of Oberyn Martell's later life: his paramour of many years, mother of the youngest four of his eight daughters, welcomed at Sunspear's high table as no baseborn woman would be seated anywhere north of the Red Mountains. The tale introduces her at King's Landing as Oberyn's equal partner in appetite and in company, unbothered by the court's scandalized arithmetic, and the pair of them — easy, loyal, incapable of jealousy — are the story's one working advertisement for love as the Dornish practice it.
The duel makes her a widow in all but law, and here the two tellings take her by opposite hands. The show forges her into its instrument of Dornish vengeance: convinced that blood must answer blood whatever the law says, she gathers Oberyn's daughters into a conspiracy that spares no one — not the innocent princess in the Water Gardens, whom she kills with a poisoned farewell kiss, and not the ruling family of Dorne itself, whose prince she cuts down in his chair for the crime of patience. Handing Dorne's spears to Daenerys Targaryen, she sails into the war she demanded — and into the path of Euron Greyjoy's fleet, which delivers her in chains to the queen whose daughter she poisoned.
The books' Ellaria is that woman's photographic negative, and her one great scene is an argument against everything her show-self does. Standing before Doran with the Sand Snakes crying for war, she asks the question the saga never improves on: where does it end? Oberyn wanted vengeance for Elia — and if Gregor dies, and Tywin, and Cersei, and the children after them, whose turn does it become, and which of her four daughters must die to keep the wheel turning? She wants her girls to bury her old and fat, not the reverse; she loved Oberyn with everything and will not feed his children to his ghost. Then she withdraws from the war party altogether — the sanest voice in Dorne, walking out of the room where the plot is being written.
In the books' telling
Oberyn's paramour, a bastard of House Uller and mother to four of his Sand Snakes — who, in the books, is the one voice begging Dorne AGAINST the war of vengeance: she has seen where it ends.
The page and the screen
No character was more completely inverted by adaptation. Book Ellaria is the voice against the war of vengeance — her 'where does it end' speech to Doran is the books' moral summary of the entire revenge theme — while show Ellaria murders a princess, a prince and Dorne's line of succession to start that very war, a rewrite so total that the two versions share only a name, a lover and a birthplace. The show also compresses the family tree: its Ellaria is mother-figure to all three Sand Snakes, where the books give her only the four youngest of eight, none of the three the show kept. Her show fate — chained in the Red Keep's black cells, condemned to watch her poisoned daughter's fate at close, permanent range — is Cersei's mirror-justice for Myrcella and has, like everything else in the arc, no book counterpart at all.
In the show, season by season
Season Five. In Sons of the Harpy — Wants a war Doran won't give her; recruits Oberyn's daughters.
Season Six. In The Red Woman — "Weak men will never rule Dorne again."
Where they stand, season by season
Their fate — if death has found them, it is written here. Open at your peril.
The chronicle records no death for this soul — they are living when the tale leaves them, or their ending is a page the maesters have yet to turn.