Who is Narsit from Persian Letters. Translated with an Introd. and Notes, by C. J. Betts and what is their importance?

Narsit is the black slave who writes to Usbek and informs him of the head eunuch's death. He asks Usbek to reply who he wishes to take control of the seraglio. Although Narsit received a letter from Usbek addressed to the head eunuch, he has not opened it. Usbek calls Narsit stupid for not having opened the letter.