King Arthur, a legendary figure rooted in medieval history and romance, is often depicted as the British leader who defended Britain against Saxon invaders in the late 5th and early 6th centuries. However, the story of King Arthur is primarily a blend of Welsh and English mythology with elements of literary invention. Most modern historians agree that Arthur is more of a mythical construct than a historical figure. Early sources such as the Annales Cambriae, the Historia Brittonum, and the works of the monk Gildas provide glimpses into Arthur's supposed historical context. Additionally, references to Arthur appear in early poetic works like Y Gododdin, though these allusions remain ambiguous and open to interpretation.

Arthur's significance as a cultural and legendary figure solidified in the corpus of stories known as the "Matter of Britain." Geoffrey of Monmouth's 12th-century Historia Regum Britanniae (History of the Kings of Britain) was instrumental in elevating Arthur to international fame. Geoffrey's imaginative narrative portrayed Arthur as a heroic warrior who defended Britain from both human and supernatural foes. Earlier Welsh and Breton tales, predating Geoffrey's work, often described Arthur as a semi-magical figure associated with the Welsh otherworld, Annwn. However, the extent to which Geoffrey relied on earlier sources versus his own creativity remains unclear.