Oberyn Martell is the cunning prince of Dorne, one of the Seven Kingdoms in Westeros. He has a score to settle with the Lannister clan, after his sister Ella was brutally murdered by Gregor "The Mountain" Clegane (Conan Stevens). In Season 4, he arrives in King's Landing to avenge his sister's death. Here's what series creators and executive producers David Benioff and D.B. Weiss had to say about the character in a joint statement.
"This was a tough one. The Red Viper is sexy and charming, yet believably dangerous; intensely likable, yet driven by hate. The boys love him, the girls love him, and he loves them all back. Unless your last name is Lannister. We found a fellow who can handle the job description and make it seem effortless. He wasn't easy to find and he won't be easy to stop."