with whom he was married to?
Guinevere
King Arthur
Many elements and incidents that are now an integral part of the Arthurian story appear in Geoffrey's "Historia", including Arthur's father Uther Pendragon, the magician Merlin, Arthur's wife Guinevere, the sword Excalibur, Arthur's conception at Tintagel, his final battle against Mordred at Camlann, and final rest in Avalon. 
when were the tales of king arthur written 9th-century who was he? He was a legendary British leader.
wiki:7687950
King Arthur [SEP] Introduction
Geoffrey depicted Arthur as a king of Britain who defeated the Saxons and established a vast empire. Many elements and incidents that are now an integral part of the Arthurian story appear in Geoffrey's "Historia", including Arthur's father Uther Pendragon, the magician Merlin, Arthur's wife Guinevere, the sword Excalibur, Arthur's conception at Tintagel, his final battle against Mordred at Camlann, and final rest in Avalon.