Sir Kay is the son of Sir Ector who, and at the beginning of the film, is training to become a knight. Kay serves as a foil to Arthur, being self-centered, boorish, and lazy, 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. 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.
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.
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, 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 to be enchanted, he attempts to fight a mop but is quickly defeated. 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 Sir Ector forbids Arthur from becoming his squire and further suggests that Sir Ector box Arthur's ears. Kay and Sir Ector then leave Arthur in tears and Kay cuts the mop handle telling Arthur, “And that’ll teach you to pop off, you little pipsqueak.”
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 insisting "Anyone can pull it once it’s been pulled.”
When he fails to pull it out, Arthur is allowed the chance to prove he pulled 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 Sir Ector begs Arthurs forgiveness.
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 similar to the way 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 main character for Don Bluth's video game Dragon's Lair, Dirk Daring, appears to have been modeled after him.