What makes Montresor such an effective enemy of Fortunato is his resolve to get revenge, attention to detail, and ability to act amicably to Fortunato's face while plotting his death. Montresor begins by mentioning he has vowed to get revenge on Fortunato for causing him to suffer a thousand times and laughing at his respected family name. Montresor then elaborates on his feelings concerning the perfect revenge and is careful not to get caught. After carefully plotting his revenge, Montresor conceals his hatred and is friendly to Fortunato's face, which allows him to convince his enemy to follow him into his family's catacombs. Montresor says,
"I gave Fortunato no cause to doubt me. I continued to smile in his face, and he did not understand that I was now smiling at the thought of what I planned for him, at the thought of my revenge" (Poe, 1).
Montresor is also aware of his enemy's weaknesses, which are pride and a love of alcohol. By mentioning that he will consult Luchesi about whether or not he has purchased amontillado, Montresor is able to pique Fortunato's interest and provoke him simultaneously. Montresor also makes sure his estate is empty by lying to his servants, which leaves him alone with his vulnerable enemy. After Montresor successfully buries Fortunato alive, he keeps his secret for half a century, ensuring that he will not be punished for his crime.
The character Iago in Shakespeare's Othello is similar to Montresor in that he carefully plots revenge and feigns friendship to Othello's face. Although he does not directly kill Desdemona, he accomplishes his goal of ruining Othello through manipulation and lies.