Oberyn Martell is the Prince of Dorne and brother to Elia of Dorne, the murdered wife of Rhaegar Targaryen . He is named the Red Viper for using a poisoned sword to kill a man in a duel to first blood. He rides to Kings Landing to attend the wedding of King Joffrey, but also seek justice for his murdered family members. However Tywin Lannister refuses to give up Ser Gregor Clegane , The Mountain That Rides, because he is such an effective murderer. So Oberyn decides to act as champion of Tyrion Lannister against Ser Gregor in hopes to attain the revenge he yearns. He uses a spear covered in poison, the spear being the sigil of house Martell, to counter the arm span of Gregor and his own speed to counter the Mountains ferocity. He shouts "Elia of Dorne you raped her, you murdered her. You killed her children." After wearing down the Mountain he goes in for the kill and stabs Ser gregor through the chest, but as he stands over him, The Mountain, pulls him down, tells him how he murdered Elia, then bashes his skull in with a fist.