player of thrones article from winteriscoming.net
Oberyn and the Martells are from the land of Dorne, specifically, the Great City of Sunspear. Dorne is the most southern territory on the continent of Westeros and is ruled by the Prince of Dorne, Doran Martell. The Martell’s sigil is a field of Orange, a sun in splendor gules pierced bendwise by a spear. Their words are Unbowed, Unbent, Unbroken
Oberyn Martell Profile
Elia Martell, Doran and Oberyn’s sister, was wed to Rhaegar Targaryen, King Aerys II Targaryen’s son and heir to The Iron Throne. During Robert’s Rebellion Rhaegar was killed, The Lannister Army sacked King’s Landing and killed King Aerys II. During the Lannister invasion, Elia Martell was raped and killed by Ser Gregor Clegane (The Mountain). In addition, Rheagar and Elia’s two children were brutally murdered in an attempt to rid the kingdom of all Targaryens and kill the Targaryen blood line.
Oberyn became furious, and wanted to raise up the Dornish Army to march on the Lannisters and Baratheons in King’s Landing. Jon Arryn, the standing hand of the king, negotiated with the Dornish Princes to prevent further bloodshed.
As you could imagine, time has not healed these open
wounds, and Prince Doran despises the Lannister name. When he was sent the invitation for the Royal Wedding (Joffery and Margaery) he decided to send Prince Oberyn in his place. Oberyn arrives in King’s Landing with his paramour Ellaria Sand (Sand is the b*stard surname in Dorne), and quickly states that he has not only come to attend the wedding, but to seek justice for what Ser Gregor Clegane and the Lannisters have done to his family.
"…the Lannisters aren’t the only ones who pay their debts."