Laughing, the Green Knight explains to Gawain that he is actually the same lord of the castle where Gawain spent his holidays. The first two blows, he claims, were in return for the way Gawain returned the kisses of his wife, following the rules of their game as an honest man should. The third blow, he says, was for Gawain’s failure to return the green girdle to him on the last day. But because Gawain’s failing was only because he wanted to save his life, and not because he's just dishonorable, the Green Knight forgives him. He leaves Gawain with only with a scar and a girdle as a reminder of his very human sin.
Another major theme in the poem is the perversion of stereotypical gender roles. Because Dame Ragnelle is a hag with no manners, she falls out of the expected female role. While Gromer is attempting to regain control of the land that he claims should be his, Dame Ragnelle simply circumvents the system. She manipulates Gawain with information in order to marry into a more desired class with a title, at which point she no longer needs to regain her family's land which would have gone straight to the male heir, Gromer, regardless. Ragnelle's power over others and in society generally increase through the poem; some scholars suggest she becomes more masculine in behavior and status as a result. In this reading her production of a male heir symbolizes the final stage or her gender perversion. 
About all we know about him is what can be gleaned from the poems. The dialect is that of the north west Midlands of England. The content reveals someone who was familiar with aristocratic life, who took both Christianity and chivalry seriously, though not without a wry sense of humor and a well-honed sense of the ridiculous. This is an author who could go against medieval prudishness and present God praising sexual love (within marriage) in his poem Purity and who could flout all the romantic conventions of courtly love, presenting Gawain as a knight both chivalrous and chaste (but oh, all too human.)