This person isn’t a character. He is more a device of the plot that helps drive the action. In the story, he’s Fortunato’s rival in wine tasting. In all, the narrator doesn’t need Luchesi in telling about the murder (for this reason Amontillado is enough). Luchesi is more kind of insurance for Montresor. He brings Luchesi up all the time he wants to keep Fortunato distracted. But again, Montresor doesn’t need to evoke the name of Luchesi. Fortunato is not only drunk but also willing to do anything to get to the Amontillado. Montresor is just playing with him, exploiting Fortunato’s “weak points”, with a little help from Luchesi.
Luchesi in the Essays