Sir Kay was Arthur's foster brother and his earliest companion as well as among the first to support Arthur's cause. Kay is an interesting figure because he starts out as a very true and noble knight but is gradually reduced to a disagreeable and treacherous character that turns against his fellow knights, even turning against Arthur near the end.

Although he is favorably portrayed as symbolizing Arthur's conscience, even acting as a guide or mentor to him at the beginning of Arthur's career, Kay degenerates into a spiteful braggart and an enemy of the king as events unfold. He embodies the best and the worst of knightly behaviour.

What do we know about Sir Kay as an actual living person? Historically it is difficult to determine his origins, if he really existed at all. Some sources place him in Caer-Gynyr near Bala in Penllyn, which he supposedly re-named Caer Gai in the early 6th century. In the Mabinogion, he is named as Lord of Caer Goch (Pembrokeshire, Wales), Cai Hir (born @ 468), eldest son of Cynyr Ceinfarfog. In many accounts he is described as "Kai the Tall". In fact he gained a reputation as a slayer of giants probably because of his own size.

In mythical accounts, he is credited with the ability to shapeshift into whatever form he wished. The Mabinogion tells us "Kai had this peculiarity, that his breath lasted nine nights and nine days under water, and he could exist nine nights and nine days without sleep. A wound from Kai's sword no physician could heal. Very subtle was Kai. When it pleased him, he could render himself as tall as the highest tree in the forest. And he had another peculiarity - so great was the heat of his nature that when it rained hardest, whatever he carried remained dry for a handbreadth above and a handbreadth below his hand; and when his companions were coldest it was to them as fuel with which to light their fire."

On the good side, Sir Kay is one of the main heroes in the tale of Kulwych and Olwen. In the Mabinogion, he was the faithful companion of Bedwyr Bedrydant (of the Perfect Sinews). He appears in the ancient Welsh poem Pa Gur in the Battle of Tryfrwyd, fighting against Garwlwyd but no one can prove exactly where this battle took place. In Welsh literature he is also found in the Dream of Rhonabwy. His title in Triads is "One of the Three Diadem'd Chiefs of Battle."

He is usually given the title of Arthur's seneschal - an official in a noble household who is in charge of domestic arrangements and the administration of servants; a steward or major-domo. It has been suggested that his name "Cai" derives from the Roman Latis "Cais" which would have been something like a tax collector in the Roman provinces. In Mallory's "Le Morte" Kay was given a lifetime position as Arthur's seneschal at the request of Ector.

Some of Kay's more heroic ventures begin in the great tournament that was held in celebration of Ban and Bors alliance with Arthur. Kay won the victor's prize. His name leads the list of champions in many battles. Shortly after Arthur's wedding, just before the invasion of the five kings, Kay counseled Arthur in strategies but Arthur chose to ignore Kay's advice. Consequently he was forced to flee - but Kay confronted and defeated two of the kings, which gave Arthur a chance to rally his forces and turn the battle around to his favor. For this, Kay was made a Knight of the Round Table.

On the bad side, his worst hostility was demonstrated towards Sir Gareth, the brother of Gawain. When Gareth came to Arthur's court to seek a position, as seneschal Sir Kay was supposed to give him all the best of food and drink and tgreat him "as though he were a lord's son." But instead he insulted him, gave him the name of Beaumans (Pretty Hands) and sent him to the kitchen. Gareth labored for a year and then he requested knighthood. Again Sir Kay insulted him by calling him an unworthy "kitchen knave." Later on, however, Gareth gets revenge by knocking Kay off his horse and taking his sword away.

In the Grail tales, Sir Kay takes out his resentment of Percival's arrival at the royal court by beating up a dwarf and a young woman. Percival is forced to leave the court because of Kay. He was always stirring up trouble with the other knights, especially baiting the younger ones into dangerous deeds - but they usually succeeded, which made Kay even more bitter.

The two sides of Sir Kay offer a lot of room for speculation as to why his image was tarnished through time and what he was really like.