Montresor, of course, is not a real person. Poe created a character who would have exactly the qualities he needed in a person who would commit the crime that his character will commit. Montresor is proud and vindictive. He is extremely intelligent and extremely cunning. He is sadistic. He is patient, willing to wait for a long time for the perfect opportunity to put his plan into effect.
Poe does not say so, but there is an implication from the way Montresor talks about Italians dealing with millionaires in art and jewels that both Montresor and Fortunato make their livings by trading in expensive merchandise such as paintings, jewelry, ceramics, antiques, and wines. The exact location of the story is not specified, but it can only be the port city of Venice, whose splendor is based on trade. The mention of palazzos helps to identify the locale.
One especially noteworthy aspect of Montresor's character is that he is poor. He is very sensitive about his poverty because of his family pride. Fortunato is rich. Since they are competitors, Montresor must have been beaten out of many transactions because Fortunato was able to outbid him. These are likely some of the "thousand injuries" Montresor has suffered at the hands of his "good friend." Fortunato entertains lavishly. Montresor must have suffered frequently from not being invited to certain gala affairs. Social snubs of various kinds would be among the "thousand injuries." Montresor is especially sensitive to social injuries because of his chronic financial distress.
Fortunato is interested in the Amontillado because Montresor says he got a bargain on a "pipe" of 126 gallons. Fortunato is thinking he might be able to buy a much larger quantity and make a lot of money. One good thing about wine as merchandise is that it doesn't deteriorate with age but only gets better if it is stored in wooden casks. Fortunato could take his own time about selling off the wine--but he has to make sure it is the real Amontillado.
It is impossible to read "The Cask of Amontillado" without thinking that Poe must have been projecting his own feelings into Montresor. Poe was adopted and then disowned by a wealthy man. Poe acquired upper-class tastes and then had to struggle to earn a living for himself, his very young wife, and her mother. He must have suffered a thousand petty injuries as he tried to maintain a position in society, and he had many enemies whom he might have fantasized about killing.
Montresor was Poe's creation. He was exactly the kind of person who could and would commit the crime he committed for the reasons he expressed.