“Nay, here I crave no fight, in sooth I say to thee,
The knight about thy board but beardless bairns they be,
An I were fitly armed, upon this steed so tall,
For lack of strength no man might match in this hall!
Therefore within thy court I care a Christmas jest,
‘T is Yuletide, and New Year, and here be many a guest,
If any in this hall himself so hardy hol,
So valiant of his hand, of blood and brain so bold,
That stroke for counter-stroke with me exchange he dare,
I give him of free gift this guisarme rich and fair,
This axe of goodly weight, to wield as he see fit,
And I will bide his blow, as bare as here I sit.
If one will test my words, and be of valiant mood,
Then let him swiftly come, and take this weapon good, –
Here I renounce my claim, the axe shall be his own –
And I will stand his stroke, here, on this floor of stone,
That I in turn a blow may deal, that boon alone I pray,
Yet respite shall he have, a twelvemonth, and a day.
Now quickly I thee crave - Who now hath aught to say?”
Such was the Green Knight's challenge upon barging into the Christmas Feast of King Arthur's Round Table. Only Gawain was brave enough to take him up on this offer, and he smote the knight's head from his shoulders. The Green Knight then picked up his head, promised to uphold the bargain the following year, and strode out. This spectacle was the work of Morgan le Fay, and the Green Knight, Bertilak, was to cause such shock to the court as to distress Guinevere. Bertilak received a magic belt in order to accomplish his task, which would allow him to overcome even the most grievous of wounds. Rather than follow Morgan le Fay's orders exactly, he instead sought to test the Knights of the Round Table and see who among them was worthy.
A year from this event, Gawain came to the location that the Green Knight had given, Castle Hutton. There he was received by Bertilak, who gave him a place to rest and prepare for the coming trial, all the while keeping hidden his true identity. He and his wife placed upon Gawain another test, with his wife attempting to seduce the knight, and in return for his food, Gawain would give Bertilak what he himself had received during the day. Gawain committed no infidelity, but on the third day was given a girdle by Bertilak's wife, which the knight did not give to Bertilak at the end of the day.
The next day, Gawain left the lord's residence for the Green Chapel. He met the Green Knight there and prepared to receive his blows, kneeling. The Green knight gave him two feinted blows and lightly nicked his neck on the third one. The Green Knight then revealed himself to be Gawain’s host. He explained that the two feinted blows were for the days that Gawain faithfully turned over the kisses from Bertilak's wife, and the nick was for not turning over the girdle. He then considered the matter settled, gifted his magic belt to Gawain and bid him to return to Camelot.
It should be noted that there are several other knights in green faced by Arthur and his knights. It is from one of them Sir Bredbeddle, a stalwart companion of the Knights of the Round Table, that Bercilak has acquired his "reindeer".