Obara Sand
The eldest of Oberyn's bastard daughters, the Sand Snakes: hard, angry, and deadly with the spear her father put in her hands as a girl.
The fuller tale
Obara is the eldest of Oberyn Martell's eight bastard daughters — the Sand Snakes, and the whole of Dorne knows the name is a boast, not a slur — and the one who wears the origin hardest. Her mother was an Oldtown whore; Oberyn came for the girl when she was small, and both tellings preserve the choosing he offered: her mother's tears on one side, his spear on the other, and Obara took the spear and never looked back at the weeping. It made her the plainest and hardest of the sisters — big-boned, quick-tempered, contemptuous of silk and of subtlety alike — and the books arm her to match: spear, shield, and a coiled whip on her saddle, weapons for a fight she has been waiting her whole life to be given.
Her father's death is the permission she was waiting for. In the books she storms into Doran's presence demanding an army — let her take Oldtown, let her burn the Reach's pride as payment on Elia and Oberyn both — and is refused, confined, and finally redirected: the prince sends her riding escort to hunt the rogue knight Darkstar, a leash disguised as an errand, with Areo Hotah instructed to watch her the whole way. The show gives her rage a freer road and a coup at the end of it; the books keep her circling her uncle's patience, the eldest snake still unstruck.
The page and the screen
The books count eight Sand Snakes; the show kept three, and Obara's promotions came with rewrites. Her book arsenal and errand — the Darkstar hunt, alive in the published pages — vanish in favor of the show's coup plot, in which she helps murder her cousin Trystane, a kinslaying the books' Obara, whatever her temper, has never been offered. The spear-or-tears story survives both tellings nearly intact, one of the adaptation's few Dornish keepsakes. Book readers note the irony of her screen fate belonging to a plot her book self would likely have endorsed loudly and been locked in a tower to prevent.
Where they stand, season by season
Their fate — if death has found them, it is written here. Open at your peril.
The show: Slain at sea (S7·E2)
Oberyn's spear-daughter met Euron's boarding party when his fleet fell on Yara's in the night. He killed her with her own weapon and left her hung from her ship's prow.
The show ends her at sea, against an enemy her whole style never planned for. Sailing with Yara Greyjoy's fleet to ferry Dorne's army to Daenerys's war, the Sand Snakes are caught in the night ambush when Euron Greyjoy's Silence and its fleet come out of the dark with fire and boarding hooks. Obara meets Euron on the burning deck spear-first and finds the story's gleeful monster beyond her: he takes the spear from her and drives it through her middle, then leaves her body hung from the prow of the wrecked ship — a message addressed to Dorne, to Daenerys, and to anyone else considering the sea lanes. In the published books Obara Sand is alive on the road to High Hermitage, hunting a knight with her father's temper and her uncle's leash still holding.