Gauvain serves the powers-that-be of the palace. Desdemonia is his employer and he reports to her directly as he his forbidden from speaking directly to any of the Maidens (no one sees the King much anyway).
When he is nervous or edgy (which is nearly all of the time), he grins hideously. To make matters worse, when he speaks, his mouth does not move and his voice is heard from behind the person to whom he speaks. What makes this even more unnerving is how he always looks nervously at the source of the voice as if someone is there.
Otherwise he is a dutiful and polite worker, ever cleaning, cooking and maintaining the interior of the palace. If there are guests, he guides them to their rooms and often startles them with his soundless appearances (usually to bring fresh linens or to invite them downstairs for dinner).
If ever he is in peril, or is commanded to apprehend someone, he attacks with his gaze: his eyes become bloodshot as they glare at his target. The victim gets a splitting headache and hears a high-pitched scream in their ears (they must pass a Constitution saving throw each round that Gauvain stares at them or else they fall unconscious).
Gauvain knows the layout of the palace very well. He even knows about the secret doors and passageways, but rarely uses them.
He is desperately in love with Cadaveria, whom he spies on all of the time through secret rooms. He openly weeps at the sound of her voice, especially at her incantations. The Steward, Desdemonia, knows this and is waiting for the right day to use it against him if his loyalty is ever in question.