Castor
Knight in Le Morte d'Arthur, nephew of King Pelles, who recognized and sheltered the disguised Launcelot.
Castor is a knight in Le Morte d'Arthur, nephew to King Pelles, attested across two chapters in Book XII. When Castor was made knight, "that same day he gave many gowns" (Le Morte d'Arthur, Book XII, Chapter IV). Castor encountered Sir Launcelot during the latter's period of madness, when Launcelot was kept as a fool at the court: "Sir Castor sent for the fool -- that was Sir Launcelot" and "gave Sir Launcelot a robe of scarlet and all that longed unto him" (Le Morte d'Arthur, Book XII, Chapter IV).
Later, on the Joyous Isle, Castor recognized the disguised Launcelot despite his assumed identity as Le Chevaler Mal Fet. He pressed the question of Launcelot's true name: "Sir, it may well be so, but ever meseemeth your name should be Sir Launcelot du Lake, for or now I have seen you" (Le Morte d'Arthur, Book XII, Chapter VI). When Launcelot confirmed his identity, "Sir Castor kneeled down and besought Sir Launcelot of mercy: For I shall never utter what ye be, while that ye be in these parts" (Le Morte d'Arthur, Book XII, Chapter VI), pledging secrecy about the great knight's whereabouts.
All six citations come from Le Morte d'Arthur Book XII, presenting Castor in two connected episodes. In Chapter IV, Castor acts as a generous host, clothing the mad Launcelot; in Chapter VI, he demonstrates both perceptiveness and loyalty by recognizing Launcelot but swearing to protect his secret. Castor's role is subsidiary but narratively functional: he serves as a witness to Launcelot's humiliation and recovery, and his vow of silence allows Launcelot's retreat on the Joyous Isle to continue undisturbed.
Appears in: Beings, Entities in Le Morte d'Arthur, British Tradition