Sir Kay is a (former) antagonist turned supporting character in The Sword in the Stone. He is Sir Ector's son.
Sir Kay is first seen hunting a deer with his bow and arrow. He aims at the deer, but misses due to Arthur. Kay sullenly returns to the castle while Arthur travels into the forest to find Kay's missing arrow after Kay tries to hurt him and despite warning him that the forest is swarming with wolves. Back at the castle, Sir Ector scolds Kay, who is eating a bowl of chicken legs, for allowing the Wart to go alone into the forest. Kay shows little concern, stating that he is not Arthur's keeper.
When a wizard named Merlin appears, Kay notes that they should just run Merlin off, but Sir Ector shoots down this idea, fearing that Merlin would curse them if angered. A bit later, Sir Pellinore, a friend of Sir Ector's, comes with news of a tournament on New Years Day. Kay at first pays little attention, until Pellinore reveals that the winner will be King of England. Sir Ector notes that if Kay buckles down, he could be knighted in time for the tournament, and compete to win. Kay agrees, but not before Pellinore quietly notes that Kay as the new King is a dreadful thought. At the same time though, Kay is also disappointed when Sir Ector points out that Arthur will be accompanying them as Kay’s squire, outright saying that he doesn’t want the Wart for a squire. The next day, Kay is seen practicing his jousting, but it quickly becomes apparent that he is not skilled. Kay's next appearance is with Sir Ector who had been summoned to the kitchen. Having found the kitchen was bewitched, he attempts to fight a mop, but is quickly defeated. Kay thinks that they ought to run Merlin right out of their castle, but Ector quickly covers his mouth, claiming that he might cast an "evil spell" on them by turning them into stone. He is seen to be fairly pleased when Sir Ector forbids Arthur from becoming Kay's squire.
At Christmas, Kay has apparently improved enough to be knighted. When his new squire, Hobbs comes down with the mumps, Arthur is called to be the replacement. There is no other choice, and so Arthur accompanies Kay to the tournament.
Sir Kay is waiting to fight when he discovers that Arthur has forgotten his sword back at the inn. Kay threatens the Wart to bring it or not come back. When Arthur brings the legendary Sword in the Stone as a replacement, he is quick to realize it is not his, but is apparently ignorant as to what it really is. When the sword is returned to the stone, to allow Arthur to prove he pulled it, Kay shoves him aside, and tries to pull it himself. Though Kay believes that it can be pulled after someone else pulled it, he fails. He is shown to be shocked when Arthur pulls it effortlessly, and he has to be reprimanded by his father, who tells Kay to bow down to his new King.