Who are the three main characters in "The Cask of Amontillado"?

Poe's story features three characters who are named: Montresor, Fortunato, and Luchesi. Montresor is the narrator of the story, telling the tale from the first-person point of view. Fortunato is the victim of Montresor's diabolical revenge. Luchesi is mentioned in the story, but he never actually appears. Montresor uses his name as a threat to keep Fortunato moving toward his impending death. He tells Fortunato that he will let Luchesi taste the Amontillado if Fortunato is not interested in trying it himself.

There is another "character" in the story, but this one is not even named or identified. Who is the person to whom Montresor confesses? A friend? A priest? A physician? Nobody knows for sure, but many have tried to figure out this mystery.