Sir Kay

Then King Arthur called Sir Kay, his steward, and bade him tend the young man for a year as if he were a lord's son.

King Arthur's Knights The Tales Re-told for Boys & Girls Henry Gilbert

By my head, said Sir Kay, that is the same knight that met with us, for this night we were lodged within a widow's house, and there was that knight lodged; and when he wist we were of Arthur's court he spoke great villainy by the king, and specially by the Queen Guenever, and then on the morn was waged battle with him for that cause.

Le Morte Darthur: Sir Thomas Malory's Book of King Arthur and of his Noble Knights of the Round Table, Volume 2 1470

The Welsh story Culhwch and Olwen is supposed to date from the 11th century (the date is based on linguistics that I'm not qualified to comment on), and in that tale Arthur appears as a great High King with a court at Celliwig in Cernyw (Cornwall) (location unknown) and a band of famous warriors, including Cai, Bedwyr and Gwalchmai (later to become Sir Kay, Sir Bedivere and Sir Gawain).

The Anglian Tower, York Carla 2010

I go back in the house, spy Sir Kay, our big brown tiger-stripe, pick him up and carry him out to the front yard.

The First Step is Admitting You Have a Problem « Whatever 2008

And by fortune in a meadow Sir Tristram met with Sir Kay, the

Le Morte d'Arthur: Sir Thomas Malory's book of King Arthur and of his noble knights of the Round table 2003

Sir, said Sir Kay, wit you well there is some new tidings.

Le Morte d'Arthur: Sir Thomas Malory's book of King Arthur and of his noble knights of the Round table 2003

Then Sir Gaheris was wroth that Sir Kay had a fall.

Le Morte d'Arthur: Sir Thomas Malory's book of King Arthur and of his noble knights of the Round table 2003

Sir Tristram thought to be at that jousts; and so by adventure they met with Sir Kay, the Seneschal, and Sir Sagramore le Desirous; and

Le Morte d'Arthur: Sir Thomas Malory's book of King Arthur and of his noble knights of the Round table 2003

THEN there came Sir Kay, the Seneschal, unto King Mark, and there he had good cheer showing outward.

Le Morte d'Arthur: Sir Thomas Malory's book of King Arthur and of his noble knights of the Round table 2003

Dodinas, Sir Kay, Sir Griflet, and all this he did with one spear; and Sir Lavaine smote down Sir Lucan le Butler and Sir Bedevere.

Le Morte d'Arthur: Sir Thomas Malory's book of King Arthur and of his noble knights of the Round table 2003