The legendary knight who fought the Green Knight in Sir Gawain and the Green Knight was Sir Gawain.
The Middle English poem, composed in the late 14th century by an anonymous poet, begins when a mysterious green challenger enters King Arthur’s hall. He proposes a beheading game: a knight may strike him once, but must receive the same blow one year and one day later. Gawain accepts to protect Arthur’s honor.
Gawain beheads the visitor, but the Green Knight survives and reminds him to meet at the Green Chapel. The rest of the poem tests Gawain’s courage, honesty, courtesy, and ability to keep his word—qualities central to medieval ideals of chivalry.
The poem is not part of a single standardized Arthurian canon, and its Green Knight differs from ordinary human opponents. Sir Gawain is also distinct from Lancelot, Galahad, and Bors, who belong to other major Arthurian narratives.