The Green Knight is best known from the Middle English poem “Sir Gawain and the Green Knight.” In that story he appears as a mysterious figure in green armor, challenging Arthurian knights to a beheading‑for‑beheading contest. Scholars generally see him as a literary device, a test of chivalry, rather than an actual war god or cryptid. Some medievalists even suggest he may echo older Celtic motifs of nature spirits, but there is no solid evidence that a real “green‑armored” knight once rode the English countryside. So, more myth than forgotten deity, though it does stir the imagination.