Prince Olyvar Martell was the Prince of Dorne and Lord of Sunspear until his untimely death in 603 AL. He was the younger brother of Prince Robert Martell who passed away 25 years prior due to injuries recieved at a tournament. Olyvar never quite fully recovered from the death of his brother and close friend. Ellaria always reminded him of Robert.
Olyvar married Lady Cassella Dayne, Lady of Starfall, a few years before Robert's death. Together they had four children: Ellaria Martell, Trystane Martell and twins Daemon and Daeron Martell. He never remarried after her death in 592 AL.
He also had his share of bastard children, some of which he raised with his noble children at the Water Gardens. Nymeria Waters is a bastard daughter he never knew about.