Fortunato in "The Cask of Amontillado" comes across as a fun guy to be with, someone most people would definitely invite to a party. A lover of good wine and good company, and with an enhanced sense of fun, Fortunato is the kind of guy that people instinctively like to be around, even if he does give the impression that he's a bit of a fool.
If we believe Montresor, however, then there's a much more unpleasant side to Fortunato. According to Montresor, Fortunato has done him a "thousand injuries." He doesn't specify exactly what these alleged injuries are supposed to have been, but they must be serious if they've incited Montresor to kill Fortunato in such a horrible way, by walling him up alive in the catacombs.
Montresor plays upon those aspects of Fortunato's character that Fortunato presents to the world in order to get him down to the catacombs, which will be his final resting place. Montresor knows that Fortunato, as a bon viveur, will not be able to resist a drop of three of the finest Amontillado wine. He also knows that Fortunato is a bit of a fool and so can quite easily be tricked into walking straight into a deadly trap.