Who do you suppose the "You" is in the 1st paragraph of the story of The Cask of Amontillado?

"You, who so well know the nature of my soul, will not suppose, however, that gave utterance to a threat."

It's not known with certainty who the pronoun 'you' in the story refers to, and this will probably never be revealed given that the writer is long dead. However, this is open for interpretation - it could be that the protagonist, Montresor, is talking to someone, such as a priest (to whom he is confiding in). It could also be his grandson. However, the most likely option is that Montresor is writing a letter to a friend, where he is addressing that person with 'you' while telling them the story of what happened with him and Fortunado.