House Martell was founded by Morgan Martell, an Andal adventurer who settled between the mouth of the Greenblood and the Broken Arm. Morgan led the defeat of the local First Men, including Houses Wade and Shell, and the Martells ruled a strip of land fifty leagues long and ten leagues wide. They did not rule as kings, but were cautious vassals of kings from Houses Jordayne, Allyrion, and Yronwood, as well as petty kings of the Greenblood
At the time of the Rhoynish Wars, the Martells were one of the lesser ruling families of Dorne, which was a collection of feuding petty kings and lords even as the other regions of Westeros began to consolidate into larger realms. When Nymeria, the warrior queen of the Rhoynar, came with her people to Westeros from Essos in ten thousand ships, the Martell lands were dwarfed by those of House Yronwood. However, Nymeria took Mors Martell, Lord of the Sandship, as her husband and, combining their strength, the two managed to unite all of Dorne under their rule in Nymeria's War; House Nymeros Martell has reigned since.
The union of their peoples saw the Martells abandon many of their older Andal customs in favor of those of the Rhoynar. Nymeria named Mors Prince of Dorne instead of king, and their lands and title passed down to the eldest child regardless of gender. The Spear Tower and the Tower of the Sun, the towers of Sunspear's Old Palace, were built in the Rhoynish fashion.
Princess Meria Nymeros Martell
Meria Nymeros Martell was the ruling Princess of Dorne from House Martell during the invasion of Essos by Aegon the Conqueror. The Storm King, Argilac Durrandon, called her the Yellow Toad of Dorne.
Meria was around eighty years old, fat, blind, and almost bald, during her reign she did nothing of note, her son Nymor ruled Dorne instead due to her blindness.
Prince Nymor Nymeros Martell
Nymor Nymeros Martell inherited the Principality of Dorne when his mother, Meria Nymeros Martell, passed away. He ruled only for half a year before he died himself in his sleep.
He has done nothing of note other than ruling the realm for his mother for years.
Princess Deria Nymeros Martell "The Warrior"
Deria Nymeros Martell inherited the Principality of Dorne when her father passed shortly after he became the Prince of Dorne.
Deria was an excellent military commander and was also one of Dorne's deadliest warriors of the time, she let her brother Lewyn Nymeros Martell handle the affairs of the realm in her name, she would send him on diplomatic missions when required too.
Deria was aware of the situation of the realms outside Dorne, she quickly allied herself with the King of the Reach, setting aside the many hostilities between the Dornishmen and the Reachmen, further she sent her brother to Braavos with the mission to seek a treaty with Emperor Aegon, whom had finished his conquest of Essos and ruled from Braavos.
Her brother Lewyn succeeded in arranging a treaty with Emperor Aegon, having secured a non aggression pact and a trade agreement between the Principality of Dorne and the Empire of New Valyria.
The Storm Kings were severly weakened by internal struggle and the Reachmen pushing them further back from the Marches, Deria saw a chance to use the oppertunity to claim some land for the Dornishmen, after a quick war, Blackhaven had fallen into Dornish hands. However, things changed quickly, the Storm King surrendered his crown for protection from Emperor Aegon, whom gladly accepted the offer. Fearing war, Deria sent her brother to Storm's End with the goal to negotiate the castle of Blackhaven. The Durrandons were first wary of the dornish sudden change of mind, but they finally accepted the return of the castle after hours of negotiating. War had been prevented once again.