Short answers, pulled from the story.
Jean Bodel coined the term Matter of Britain in the 12th century to categorize medieval stories into three distinct groups. He declared that all stories fell into the Matter of Rome, the Matter of France, or the Matter of Britain.
The Matter of Britain is a body of legendary material centered on Great Britain and Brittany that flourished from the 12th to the 16th century. It encompasses prose and verse works exploring legendary kings such as Brutus of Troy, Coel Hen, and Leir of Britain alongside King Arthur.
Geoffrey of Monmouth became the central architect of the Matter of Britain by writing the History of the Kings of Britain in the 12th century. His work linked the founding of Britain to the Trojan War and provided a historical lineage for the Norman Conquest.
Chrétien de Troyes introduced the Holy Grail quest to the Arthurian legend while writing in Old French during the 12th century. His works added layers of complexity and Christian themes to the narrative that became central to later cycles.
19th-century scholars like Albert Pauphilet and Alfred Nutt traced the Arthurian legend to ancient Celtic mythology and folklore. They identified characters such as Morgan le Fay with the Welsh goddess Modron and Leir of Britain with the sea-god Llýr.
The Victorian revival of the Arthurian legend occurred in the 19th century after the legend had largely faded from European consciousness by the 17th century. Writers and artists in Victorian Britain sought to recapture the spirit of the Middle Ages and find meaning in the ancient tales.