Oberyn Martell is a prince and younger brother to Prince Doran, ruler of Dorne. He is also known by his nickname, the Red Viper. He is described as hot-tempered, sensual, unpredictable and shrewd. He is also notorious for his skill in battle and his knowledge of various poisons, which he apparently learned while studying under maesters in the Citadel. He is rumored to fight with a poisoned blade.
As a child, Oberyn was very close to his sister Elia, who later left to King’s Landing to marry to Prince Rhaegar Targaryen. Oberyn has always held deep hatred and contempt for the Lannisters, who he blames for the brutal rape and death of Elia and her children. Oberyn is introduced in the Game of Thrones TV show during Season 4, when he visits King’s Landing in place of his brother to attend Joffrey’s wedding. He reminds the Lannisters that it was by their command that Elia was killed, and he still seeks justice for her fate. When Joffrey is poisoned, Oberyn is chosen to be a judge at Tyrion’s trial.
Oberyn is lusty and bisexual and is shown in the TV in several brothel scenes with his paramour, Ellaria Sand. Oberyn has eight bastard daughters, four of which were by Ellaria. His daughters are nicknamed the Sand Snakes and are said to be as quick to anger as their father.
In the show, Oberyn is acted by Pedro Pascal and he has scenes starting in Game of Thrones Season 4.