In "The Cask of Amontillado," how does Montresor interact with the other characters?
There are not many characters in Poe's The Cask of Amontillado, but there are a few: aside from Montresor, there is Fortunato, Luchesi is mentioned by name only, and Montresor's absent servants.
I will save Fortunato for last, as he is the most important of the three other characters. We do not get to see Montresor interacting with Luchesi, but we can assume that he at least knows that Luchesi will serve as a good driving factor for Fortunato. The interaction between Montresor and his attendants is told to us after it was supposed to happen, but it still shows us how manipulative Montresor is because he told his servants not to leave the house while knowing full well that they would do the opposite of what he asked.
The biggest piece of information we learn about Montresor through his interactions with the other characters is that he is manipulative, which is very evident in his interactions with Fortunato. Montresor spends the entire story manipulating Fortunato all the way to the unfortunate man's death.
I will elaborate a little further on Montresor's interactions with Fortunato. Although we know that Montresor's intention for the evening is to kill Fortunato, Montresor treats Fortunato with the utmost politeness: he greets him pleasantly, shows reluctance to interrupt Fortuanto's partying, and shows concern about Fortunato's health. All of his actions are fake, but he plays the part of good friend very well because Fortunato does not expect a thing. Even as he is sealing Fortunato in the recess in the wall, he keeps up the pleasant charade, not saying a thing about what he is doing and merely continuing to assure Fortunato that the Amontillado is there; not once does he break character to tell Fortunato why he is doing this, or that there is actually no Amontillado, or even that Fortunato is about to die.