Oberyn Martell

Youngest of the three Martell siblings — after Doran, who inherited Dorne, and Elia, who married into House Targaryen — Oberyn earned his epithet young: at sixteen he was found in bed with a lord's paramour and fought a duel over the insult in which both men drew blood, and his opponent's wound turned bad and killed him within the month, giving rise to a reputation for poisoned steel that followed him the rest of his life whether or not the rumor was ever true. He traveled widely through Essos and the Free Cities in his youth, studying poisons, fighting as a sellsword, and briefly forging the first links of a maester's chain before boredom or restlessness pulled him elsewhere.

He fathered eight daughters by various mothers, all but one with his longtime paramour Ellaria Sand, and the Sand Snakes grew up as fierce and unconventional as their father. He never married.

The Sack of King's Landing in 283 AC, in which his sister Elia and her two children were killed by Tywin Lannister's men, was the grievance Oberyn carried unspent for seventeen years. When Tyrion Lannister was accused of poisoning King Joffrey and demanded trial by combat in 300 AC, Oberyn volunteered as his champion for one reason alone: the chance to face Ser Gregor Clegane, Elia's killer, in single combat and drag a confession out of him before he died.

He got the confession. He did not survive to make use of it — having wounded Gregor mortally with a poisoned spear, he lingered to demand the names behind the murder rather than finish the kill, and Gregor's dying strength was enough to crush his skull between two hands. The poison did its work on Gregor days later regardless.