I am Bertilak

   

Greetings to all who follow the exploits of good King Arthur and his Knights of the Round Table. I am the owner of a great castle several days ride from King Arthur's fort. If you seek me, I will lower the drawbridge and offer you my hospitality. I am a renowned hunter and I will share all that I gain with you. But beware if you come with a character that is not virtuous, for I am a stern judge.
     My real name is Bertilak De Hautdesert, and I dwell with my beautiful consort who sometimes helps me in my holy quest to test the worthiness of the Knights of the Round Table. My lady is my partner, my ally, and my treasure. I could not perform my duties without her. How do I test the nights? I do it with the help of another great lady who resides on my manor. Her name is Morgan Le Fay. I call her great because she is a mistress of magic. Many years ago, she was in love with Merlin the wizard. Their relationship yielded not only happiness for both but also magical powers for Morgan Le Fay. Thanks to Morgan Le Fay, I have the perfect disguise for testing the knights--I become The Green Knight.

Holly means that I come not to wage war. The battle-ax is your penance. 

      I will let you in on a secret. Morgan Le Fay is King Arthur's half-sister. She is also the daughter of Duchess Tintagel. But Arthur has a different father--Uther Pendragon. The devotion of Morgan Le Fay to her half-brother is her reason for finding a way to make sure that his knights are truly the best citizens in his kingdom. She is a loyal Briton and a loving companion for my duchess,  and I am devoted to Morgan Le Fay.  God is my ultimate sovereign, but I will support all Britons who love God and obey his laws. Therefore, I will only allow those who are virtuous, chaste, honest, and courageous to lead and protect us, to be members of the Knights of the Round Table. Although I am both terrifying and mysterious to the Knights of the Round Table, I am actually a friend in disguise. However, do not be fooled by my friendliness and my hospitality. My judgements are harsh but necessary. I am brutal but honest.
My sources are: Sparknotes, Cliffnotes, Wikipedia, and "Sir Gawain and the Green Knight."