Lord Bertilak is a character from the medieval poem Sir Gawain and the Green Knight. He is the lord of Bertilak de Hautdesert, a castle where Sir Gawain stays during his quest. Lord Bertilak is known for his hospitality and generosity, welcoming Gawain and providing him with food and shelter. In the story, Lord Bertilak plays a crucial role in testing Gawain's honor and integrity. He proposes a game where they exchange their daily winnings, which leads to a series of challenges that reveal Gawain's character. Ultimately, Bertilak is revealed to be a key figure in the larger narrative of the poem.