What is it about Montresor that makes him an especially effective enemy to Fortunato? Give an example from another book, film, or TV show in which...

Montresor is an especially effective enemy of Fortunato because he has made Fortunato and everyone who knows these two men believe that they are the best of friends. Montresor is cunning, and it is his cunning that enables him to make Fortunato believe he is his good friend. Therefore, Fortunato trusts him, and when Fortunato disappears, nobody will ever suspect Montresor of foul play because they are sure that he and Fortunato were very good...

Montresor is an especially effective enemy of Fortunato because he has made Fortunato and everyone who knows these two men believe that they are the best of friends. Montresor is cunning, and it is his cunning that enables him to make Fortunato believe he is his good friend. Therefore, Fortunato trusts him, and when Fortunato disappears, nobody will ever suspect Montresor of foul play because they are sure that he and Fortunato were very good friends.

The one character is classic literature who resembles Montresor in this respect is Iago in Shakespeare's Othello. Iago has Othello convinced that Iago is honest and that he is Othello's friend. Even after Othello has killed Desdemona as a result of Iago's villainous machinations, he speaks highly of Iago, who has completely deceived him.

EMILIA:
O mistress, villainy hath made mocks with love!
My husband say that she was false!

OTHELLO:
He, woman;
I say thy husband. Dost understand the word?
My friend, thy husband, honest, honest Iago.

A more modern instance of Montresor's type of villainy can be seen in the excellent 1998 movie The Truman Show, starring Jim Carrey. Truman Burbank discovers that he has been on an internationally popular television show ever since he was a baby, and that the woman he is supposedly married to is a professional actress working for the producers of "The Truman Show." The show relies for its income on advertising inserted in the scripted drama in what is called "product placement." Truman also discovers that the man who has been his best friend since childhood is also a professional actor who works for the show and has only been pretending to be his friend for all these years. This "friend" is as cunning and insidious as Montresor. In fact, everyone in the show is a professional actor except for Truman himself, who has been kept in ignorance all his life while being photographed from countless concealed video cameras in the totally artificial town where he grew up.