Sir Kay is the son of Sir Ector who is destined to become a knight. Kay serves as a foil to Arthur, being ungenerous, ill-mannered, and work-shy, despite being higher in rank than Arthur. Aside from usually calling him the deriding nickname of the Wart, Kay treats Arthur rather cruelly, often trying to physically attack him for his mistakes and consistently picks on him. However, at the end when Arthur becomes King, he comes to respect Arthur as the King and his foster brother. He also shows guilt for the way he treated him in the past and understands he should've been a more kind and supportive brother.
Sir Kay is based on the character of the same name from the King Arthur legends, who like the Disney character, was Arthur's adoptive brother. He is a big, muscular young man with red hair, and is most likely somewhere around the age of twenty, judging from a line from Merlin.
Sir Kay is first seen hunting a deer with his bow and arrow. He aims at the deer but misses due to Arthur falling down on top of him.
Kay tries to hit Arthur who attempts to apologize. Kay ignores it and tells him “If I ever get my hands on you, I’ll wring your scrawny little neck. So help me, I will!” Arthur goes to the entrance of the forest and hides from Kay behind a tree. To make up for the mistake, he offers to go look for the arrow, telling Kay, “I’m sure I can find it.” Kay laughs at Arthur and tells him surely he won’t go in the forest, “Why, it’s swarming with wolves.” Arthur, however, tells him, “I’m not afraid.” Kay then dismisses him, “Go ahead, it’s your skin, not mine!” 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 and demonstrates his magical abilities by causing a 'wizard blizzard', Kay is thoroughly unimpressed answering an amazed Sir Ector with, "So, what?" When Merlin begins to challenge Sir Ector by disappearing after Sir Ector shows himself against the idea of Merlin educating Arthur, Kay responds as equally as uninterested with, "Good riddance." until Sir Ector finally gives in to Merlin.
A little while later, Sir Pellinore, Ector's friend, 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 which Kay says is a "Pretty fair prize." 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 Ector points out that Arthur will be accompanying them as Kay’s squire, outright saying, "I don't want the Wart for my squire." The next day, Kay is seen practicing his jousting, but it quickly becomes apparent that he is not skilled. After the fish lesson with Merlin, Kay is seen again when he and Ector refused to believe in Arthur's true story about the fish experience, leading Ector to punish the Wart by giving him more kitchen duties as a consequence for being late and for telling them about the strange fish story. Kay goes on to further ridicule Arthur by telling Ector, "I told you the Wart was looney."
Kay's next appearance is with Ector who had been summoned to the kitchen, due to the Scullery Maid warning them about what she saw in the kitchen. Having found the kitchen to be enchanted, he attempts to fight a mop, but is no match for the enchanted dishes. When Arthur and Merlin came back to the castle and when Ector berates Merlin for putting black magic over the kitchen, Kay thinks that they should run Merlin 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. Kay is seen to be fairly pleased when Ector forbids Arthur from becoming his squire and further suggests that Ector box Arthur's ears. Kay and Ector then leave Arthur in tears and Kay cuts the mop handle and telling Arthur, “And that’ll teach you to pop off, you little pipsqueak.”
At Christmas, Kay has apparently improved enough to be knighted. When the Scullery Maid warns Ector that the new squire, Hobbs, has come down with the mumps, Arthur is called by Ector to be the replacement. There is no other choice, so Arthur accompanies Kay to the tournament in London, along with Ector and Pellinore.
Sir Kay is waiting to fight when he discovers that Arthur has forgotten his sword back at the inn. Kay threatens the Wart, "You better get it or don't you dare come back!" When Arthur brings the legendary Sword in the Stone as a replacement, Kay 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 insisting "Anyone can pull it once it’s been pulled.”
When he fails to pull the sword out, Pellinore and one of the knights, Sir Bart, suggests that Arthur should try pulling it out. When he does, Kay is seen to realize for the first time how special Arthur was and appears to regret his cruel treatment of him as he kneels down before him as Ector begs Arthur's forgiveness.
Sir Kay was seen in "Ask Von Drake" with Arthur, Merlin, and Madam Mim, trying to pull the sword out of the stone as Von Drake explains that Sir Kay sits by Madam Mim in the line "King Arthur's next to Merlin and Sir Kay's by Madam Mim."
Knowing that Merlin prophesied that Arthur shall pull out Excalibur from the stone, Sir Kay arrives their first, wanting to become the Ruler of Camelot. Arthur warns him not to take it, but Kay defies him and does so anyway. As he wasn't meant to be the one to pull it out, the sword glows and turns Kay to dust.
- The way Sir Ector accidentally bumps his sword into Sir Kay's head and Sir Kay moans in pain when trying to attack the enchanted kitchen supplies is recycled animation from when Horace accidentally bumped his club/chair leg into Jasper's head and Jasper moaned in pain when trying to attack the puppies in 101 Dalmatians, only Sir Ector doesn't get kicked in the rear by Sir Kay for his clumsiness as Jasper does to Horace because he is Kay's father and he'll get mad at him for it.
- The animation of Kay chasing Arthur and tripping over something is used twice during the film and the animation of him eating chicken legs is used three times.
- The main character for Don Bluth's video game Dragon's Lair, Dirk Daring, appears to have been modeled after him.