Montresor is vengeful, obsessive, methodical, deceitful, manipulative, and merciless. Repaying Fortunato for an unnamed "insult" that is more important than the "thousand injuries" he has suffered at his hands becomes more than just an idle fantasy. It obsesses him to a point that he devises a careful, cold-blooded, step-by-step plan to murder his enemy, leaving nothing to chance. He deceives Fortunato by playing on his vanity and trust. He picks a time, Mardi Gras, when Fortunato will be inebriated and vulnerable and lures him into the damp, isolated catacombs. Fortunato, his judgment impaired by drink, clearly does not suspect that Montresor is his enemy. In conclusion, Montresor shows no mercy as he chains up his enemy leaving him to die slowly and alone in a dark place. 

Montresor is an extremely proud man.  It is the fact that he feels so injured and insulted by Fortunato that causes him to seek the most violent and permanent revenge possible: he wants to kill his nemesis.  He is proud of his family motto, "Nemo me impune lacessit," which translates to You will not harm me with impunity.  Montresor feels wronged, and so he cannot maintain his family honor and pride unless he lashes back at the one who he feels has harmed him.

Montresor is also a very clever man.  He understands people: he knows that if he tells his servants not to leave and that he will be out all night, they will undoubtedly leave immediately.  He also knows Fortunato well enough to know that this man's pride can be used against him: Fortunato will insist on seeing the rare and expensive wine in order to gloat over the fact that Montresor was swindled; he will insist despite the danger to his health and despite the fact that another wine connoisseur is available.   Further, Montresor is careful to think ahead and dress is such a disguise that he cannot be identified later as having been seen with Fortunato.  He seems to think of everything (except the guilt he may feel later on...).

Characterize Montresor. What kind of person is he?

Montresor is an extremely proud man; he is also very clever and manipulative.  At the beginning of the story, he exaggerates the number of injuries he had sustained at the hands of Fortunato, as if to justify his murder.  He says, 

The thousand injuries of Fortunato I had borne as best I could, but when he ventured upon insult I vowed revenge [....].  At length, I would be avenged; this was a point definitely settled [...].  I must not only punish but punish with impunity.  A wrong is redressed when retribution overtakes its redresser.

His pride will not allow him to labor any more under the insults with which Fortunato has apparently assaulted him.  He must seek revenge, and it must be done in such a way that he can never be punished for it (or else it doesn't really qualify as revenge because he'd be harming himself in the process).  Montresor feels that he must live up to his family motto: "No one harms me unpunished."  He clearly feels a great deal of family pride, as he tells Fortunato, "'The Montresors [...] were a great and numerous family.'"  Because Montresor speaks in the past tense, here, we might assume that his family is no longer as great or numerous as it once was, and this might be another reason why he feels so strongly about honoring the family by upholding their motto.  

Further, he thinks he knows just how to move forward with his plan to exact his revenge "with impunity," and he very nearly does achieve it.  He is quite cunning while preparing a trap to catch Fortunato, ironically, with Fortunato's own pride.  Montresor says,

It must be understood that neither by word nor deed had I given Fortunato cause to doubt my good will.  I continued, as was my wont, to smile in his face, and he did not perceive that my smile now was at the thought of his immolation.

He wants to be sure that his auditor understands how craftily he proceeded with his plan.  Montresor tells us that Fortunato has one weak point, and though he never names it directly, we can assume that it is Fortunato's own pride, especially in his talent and taste as a wine connoisseur; Montresor says that "in the manner of old wines, [Fortunato] was sincere."  Montresor rather brilliantly exploits this one weakness in order to exact his revenge.  He engages Fortunato's pride by telling him that he bought a type of rare wine and that he was looking for another local expert to help him confirm the wine's identity, so to speak.  Fortunato cannot turn down an opportunity to showcase his talent (or rub Montresor's nose in his likely error).

What Montresor doesn't count on, however, is his own guilt.  He planned for everything except the way his own conscience might punish him.  It seems that, even though he was never formally punished for Fortunato's murder, his guilt has lingered for some half a century and this, perhaps, has actually been his punishment.  The fact that Montresor seems to be an old man now, on his deathbed, confessing the sins which still weigh heavily on his conscience, tells us that the murder has stayed with him.  He is telling this story to one who he says, "so well know[s] the nature of [his] soul," and the final Latin line that translates to "rest in peace," seems to support this reading as well.  Further, when he describes his feelings after he'd walled Fortunato in, he says, "My heart grew sick; it was the dampness of the catacombs that made it so."  This, again, sounds like someone trying to convince himself not to feel guilty, that his actions were warranted, even justified, and there is really no reason to convince ourselves that we shouldn't feel guilt if we already don't.

Thus, Montresor is quite proud, and very intelligent...just not quite as intelligent as he believes himself to be because he failed to account for the way a guilty conscience could punish him for the remainder of his life.

What kind of person is Montresor?

As the narrator of the tale, Montresor is either confessing or bragging the murder that he committed years ago. This, right away, may be used to measure to what extent he may be a narcissist or a sociopath. He may be a narcissist because it is clear that his narrative is not an act of repentance, but a return to a scene in his life for which he does not take much responsibility, and of which he seems quite proud.

He could also be seen as a sociopath who cannot connect to others, is always alone, unhappy, and whose anger at his own state is transferred onto others, who are happier, or richer, or better suited to life than he is. This being said, narcissist and sociopathic are good descriptors for Montresor. 

Stemming from those two descriptors, come the behaviors expected from those who have those mental conditions. They are all evident in Montresor. He is vengeful, envious, and so egotistical that he cannot let go of Fortunato's supposed insult. 

A wrong is unredressed when retribution overtakes its redresser.

Waiting and pre-meditating Fortunato's death makes Montresor also a predator; a cold hard killer so reactive that he does not feel any worry about possible consequences. He has been lucky enough to get away with it. He knows that, too.

It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong. 

Stewing over what he feels is "insult", Montresor also comes off as obsessive, petty, and unreliable. Even though first person narrators are often unreliable, Montresor shows that he may very well be also a mad man, for which we cannot ascertain for sure whether his story is based on reality, or on what his mind dictated him at the time.  

What kind of person is Montresor?

Montresor is a character created by Edgar Allan Poe to fulfill a purpose. He must be the kind of man who would commit a terrible murder. Poe has made him intelligent, proud, patient, cunning, deceitful, and cruel. His French name suggests that he is an outsider in the Italian city where he lives, which is presumably Venice. He lives in a palazzo, but he is all alone and has a hard time keeping up appearances and making ends meet. He appears to deal in expensive things like works of art, antiques, jewelry, and gourmet wines. He is an aristocrat but in constant danger of losing his social position if he fails to earn enough money.

It should be obvious that in many respects Montresor is like Poe himself. Poe may have written "The Cask of Amontillado" in order to express some of the hatred he felt towards some real person who had offened him. He had numerous enemies because of his petulant nature and his caustic literary criticism. Both Poe and his character Montresor seem like lonely, bitter, unhappy men, and both seem to have been overly fond of liquor.

What kind of person is Montresor?

Montresor is the narrator of "The Cask of Amontillado" by Edgar Allan Poe. The story is written in the first person, enabling us to see the events of the story through Montresor's eyes and also to observe his thought processes. 

The first thing we learn is that Montresor is vengeful. He hates Fortunato for some real or imagined wrong Fortunato did to him in the past and not only desires revenge, but does so in a manner that is an obsession. We never learn what the wrong was, or whether it was real or imaginary.

Next, we know that Montresor is from what is (or was) a powerful and wealthy family, possessing a large home with servants. He is also cultured and is a connoisseur of fine wines and a snob, proud of his own cultural superiority. 

Finally, he is very self-controlled, able to lie easily and without remorse, and skilled at manipulating people. He has a sadistic streak, taking a certain degree of pleasure in the pain of others.