The protagonist is Montresor. The antagonist might be said to be Fortunato for the sake of comparison, although the antagonist might also be the forces of the law which Montresor has to circumvent in order to obtain the revenge he seeks.
Fortunato is rich and has widespread family connections in Italy. Montresor is poor and alone in the world. Poe makes it clear that Montresor is of French descent and considers himself French though his family has lived in Venice for a long time. Montresor hates Fortunato but conceals his hatred behind a mask of friendship. It would appear that both men earn their livings by dealing in such expensive items as oil paintings, antiques, jewelry, and gourmet wines. Fortunato is witty and fun-loving. Montresor is serious and gloomy. He is capable of conceiving and committing a horrible murder. He may be somewhat insane. Both men are intelligent and shrewd. Both like to drink. Montresor claims that he has suffered a "thousand injuries" at the hands of Fortunato, but there has been much debate about whether these are real or imaginary.
Montresor entices Fortunato into his catacombs by telling him he has just purchased a large cask of Amontillado (Spanish sherry) at a bargain price. The whole story deals with Montrsor's psychological and logistical problems in getting Fortunato to the place where he can chain him to the granite wall and leave him to die.