The Green Knight’s true name is Bercilak de Hautdesert one of the most powerful knights in Arthur’s realm. Transformed into the Green Knight by Morgan le Fay in order to test Arthur’s court.
The Green Knight appeared before the court during a feast, and was described as being completely green: skin, hair, dress, and all. He holds a bough of holly in one hand, and an enormously menacing battle axe in the other. He is dressed in garments, signifying his peaceful approach as he does not intend for violence, however, the knight issues a challenge: he will allow one man to strike him one time with his axe, under the condition that he be allowed to return the blow the following year. At first, Arthur takes up the challenge, but Gawain pulls him aside and pleads for him to give him the opportunity. Arthur gives him a chance and Gawain accepts the challenge. In one swoop, to the exposed neck of the Green Knight, he decapitates the giant, only to have the strange Knight calmly stand, retrieve his head, and tell Gawain to meet him at the Green Chapel at the stipulated time.
The next time the Knight appears, he is in the form of Bercilak de Hautedesert, lord of a large castle, who freely invites Gawain to lodge there as he prepares to complete his journey to the Green Chapel. Gawain, unaware of his lord’s true identity, is submitted to a series of tests of his loyalty and chastity (Bercilak even sends his wife to seduce Gawain). Bercilak arranges a wager with the unknowing Gawain to hand everything that he receives that day over to the other man; they toast a drink to the agreement. But, as the time approaches for Gawain to meet with the Green Knight, he asks to depart and is asked by Bercilak not to leave just yet. Fearing that he will not make it, he asks if his host knows where the Green Chapel is located. The King knows of its location and tells him that it is a mere two miles away; Gawain agrees to remain for a few more days, enduring the tests until his departure. Gawain departs to the Green Chapel, which is really a mound of grass. When Gawain arrives, the Knight is sharpening his axe. Gawain bends to receive his blow, only to have the Green Knight feint two blows, then barely nick him on the third. He then reveals that he is Bercilak, that he sent his wife purposely to test Gawain, and that Morgan le Fay had given him the ability to be the Green Knight in order to test Arthur’s court. He and Gawain part on good terms.
Latter the Green Knight appears as as one of Arthur’s knights. He offers to help Arthur fight a mysterious sprite (under the control of the magician, King Cornwall) which has entered his chamber. When physical attacks fail, Bredbeddle uses magic to subdue it. The Green Knight eventually gains so much control over the sprite that he convinces it to take a sword and strike off its master’s head.
D&D 5E Epic Monsters: Green Knight
His name sometimes changes depending on the story (along with a few other details), but they all establish the Green Knight as a central character to the Arthurian myths, a teacher of sacred things and tester of other Knights of the Round Table. During a Christmas feast he appears and challenges the court to a beheading game: strike him once with his axe, and a year later he’ll return the strike. King Arthur volunteers but Gawain insists otherwise then decapitates the Green Knight—who picks up his own head, puts it back on, and promises to meet again at the Green Chapel in a year’s time.
Their next meeting is sooner than Gawain realizes however as his host on the way to the declared site (Bertilak de Hautedesert) is actually the Green Knight. Gawain’s chastity and loyalty are tested while in Bertilak’s castle, resisting the seductions of his wife, and the warrior agrees to exchange prizes from hunting in the area nearby. When New Year’s Day arrives Gawain goes to the Green Chapel to honorably suffer what was promised—and the Green Knight spares Gawain three times before revealing his other identity.
This is also when he relates other information that changes based on the specific retelling (that he was sent by Morgan le Fay, or by his mother-in-law). One of the more interesting tales has him helping King Arthur fight a sprite loose in the castle, using a scroll of some kind to take control of it and send it back to attack its conjurer (King Cornwall).
Medium humanoid, lawful neutral
Armor Class 18 (plate)
Hit Points 102 (12d8+48)
Speed 30 ft.
Saving Throws Con +7, Wis +5
Skills Deception +8, Insight +5, Perception +5, Persuasion +5, Religion +6
Condition Immunities charmed, frightened
Senses blindsight 30 ft., passive Perception 15
Challenge 8 (3,900 XP)
False Identity. The Green Knight can remove his armor and assume his other identity as Bertilak de Hautedesert, gaining advantage on Charisma (Deception) checks made to conceal that he is the Green Knight.
Headless. The Green Knight can survive without his head.
Regeneration. The Green Knight regains 10 hit points at the start of his turn if he has at least 1 hit point.
Relic Worker. The Green Knight has advantage on Intelligence (Religion) checks made to interpret spell scrolls, and can use any divine spell scroll.
Multiattack. The Green Knight attacks three times with his greataxe or handaxes.
Green Greataxe. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d12+4) magical slashing damage. When the Green Knight scores a critical hit against a creature that has at least one head, the creature makes a DC 15 Strength saving throw or he cuts off one of its heads. The creature dies if it can’t survive without the lost head. A creature is immune to this effect if it is immune to slashing damage, doesn’t have or need a head, has legendary actions, or the GM decides that the creature is too big for its head to be cut off with this weapon. Such a creature instead takes an extra 30 slashing damage from the hit.
Handaxes (3). Melee or Ranged Weapon Attack: +7 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 7 (1d6+4) slashing damage.
Heavy Crossbow. Ranged Weapon Attack: +3 to hit, range 100/400 ft., one target. Hit: 5 (1d10) piercing damage.
Parry. The Green Knight adds 3 to his AC against one melee attack that would hit him. To do so, the Green Knight must see the attacker and be wielding a melee weapon.
Bernlad also known as Bertilak, Bercelak, a warrior of fiercely independent disposition, is one of the few powerful lords who has not sought a chair at the Round Table. He rode into Arthur’s court in bright green armor and challenged any man to hit him with his axe. When Gawain accepted this challenge and beheaded him in one stroke, Bernlad simply picked up his head and left, instructing Gawaine to present himself for a similar stroke in a year.
True to his word, Gawain sought out the Green Knight and presented himself for the return stroke. After a series of tests designed to test Gawaine’s virtue, Bernlad merely nicked the valorous knight and discharged the obligation. Gawain was helped by Lady Bertilak by the wearing of a protective sword sheath, or baldric and so although Gawain was successful in defeating and beheading the Green Warrior/Bertilak, he was then forced to wear the green baldric also known as , the to indicate his success was a result of someone else’s help
The Green Knight was the victim of an enchantment brought about by the work of Morgan le Fay. Here Bertikak questioned Arthur upon the issue of women’s desires, and what it was that they most longed for! Ragnell was prepared to provide Arthur with the answer only if, in return, the Gawain would marry her
The secret of Bernlad’s immunity to harm lies in his Green Armor, which was given to him by the Lady of the Lake in order to test the virtue of Arthur’s court. As long as Bernlad wears the armor, he cannot be harmed by any physical weapon. This enchantment applies only to him. In addition, Bernlad’s battle axe is a +3 weapon.