Montresor is a man obsessed with revenge. He also seems to be rather insecure and sensitive, especially about his family background. For example, he says his reason for killing Fortunato is that Fortunato insulted him. This insult seems to revolve around his family's background. Fortunato makes reference to this when he says, "Of I forgot. The Montresors were a once a great and noble family." Fortunato also makes the sign of a mason, a secret organization of wealthy men. When Montresor obviously doesn't recognize the sign, Fortunato says, Oh, you are not of the masons?" Montresor replies by showing a trowel, a tool of a common mason and using a play on words,tells Fortunato, "Yes. I'm a mason." Montresor is also a cunning observer of people. He has deduced that one of Fortunato's flaws is his pride in knowing about fine wine. He constantly baits Fortunato with the line,"Well, I can always get Luchesi." This hurts Fortunato's pride so he continues on through the catacombs. Montresor, himself, is also proud. He is proud that he planned revenge on someone who insulted his family and he's proud that no one has discovered his crime for 50 years.
There are many ways you could describe Montresor. He was a man who wanted vengeance and would go to horrible means to get it. He was also a very clever man. One can not say he wasn't very intelligent.
"The thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult, I vowed revenge." From this one quote, we see that Montresor is seeking revenge against one of his "friends". We never know what the thousand injuries are, or what insult he is talking about, all we know is that Montresor is going to make Fortunato pay for his so called crime. The plans that Montresor has for Fortuanto are horrendous. We see that Monstresor has no problem burying a man alive. Montresor is a person who has no conscience at all. He does not feel guilty for what he has done. He is confessing his crime to an unknown person, but he is not asking for absolution, he is almost giddy with what he had done. We see that he as an arrogant attitude because he did 50 years earlier, and has never been caught. He is a typical serial killer. He is also extremely intelligent. He has killed before and never been caught, so this means he was really smart. He was able to commit these horrible crimes and continue to get away with it.
Poe created such a psychotic character in Montresor, yet we are invested in him. We want to see what he will do next.
The easiest way to describe Montresor would be as vengeful, single-minded, and unforgiving. We know from the very beginning of the story that he is intent on exacting revenge for the “injuries” and “insults” of Fortunato, and that he is patient, willing to wait “at length” for an opportunity to arise to allow him to achieve his end. He does not once waver in his plan to murder Fortunato, hesitating only once as he is bricking up the recess in which Fortunato is chained; and even then he hesitates not out of indecision, but out of fear that Fortunato has escaped his bindings. And consider the Montresor family’s motto: Nemo me impune lacessit—“no one attacks me with impunity.” Here we have confirmation that the man is vengeful, and learn that this vengeance is rooted in his family’s values and history. The man is proud—he comes, after all, from “a great and numerous family,” with a reputation that he is burdened with upholding.
Given Montresor’s unerring performance in tricking Fortunato into his cellar and his chosen method of murdering his “friend,” we can confidently say that Montresor is a creative man, and clever. His tactics involve a good amount of knowledge about his acquaintances—he knows that Fortunato, a “quack” in many ways, is a genuine connoisseur of wine, and that he believes Luchresi to be “an ignoramus” who “cannot tell Amontillado from Sherry.” Montresor plays off of Fortunato’s own biases and pride to lure him deeper and deeper into his trap, until there is no escape. The fact that Fortunato is led very deep into Montresor’s cellar without having any doubts or suspicions about the events at hand is testament to Montresor’s acting abilities—all this time, harboring the most sinister of intentions, he manages to disarm Fortunato and maintain a friendly demeanor. Also, we know that Montresor is never punished for his crime, which indicates that he feels little to no guilt, and that he has a very strong command of his emotions, such that he can keep his secret and raise no suspicions for decades after the crime is committed.
Montresor is a scheming and intelligent man, patient and careful. He is true to himself and loyal to his family’s legacy, unafraid—indeed, determined—to do anything necessary to free his name from what he perceives as unjust insult. He is strong-willed and innovative, utilizing the resources available to him to maximum effect. And, of course, he is a murderous villain.