We have a mad protagonist named Montresor and a drunk antagonist named Fortunado,which means luck-adverse to his bitter end.Montresor begins his story by mentioning to an unknown person/thing about a vow of revenge for the insult of Fortunado.Planningly,in the feast time for Dionysos,Montresor takes Fortunado to his underground cellar by saying he'll take him at where the famous wine Amontillado is present.They have conversation including foreshadowings,ironies and puns.Drunk Fortunado gets aware of his tragic occasion only when he's walled up by Montresor among Montresor's family catacombs.With this horrible scene and murder style,we see how grim the mankind can be when they feel offended psychologically.
In the story,we're not able to find any specific sign proving Montresor's being insane.However,from the symbols,narrating style and the bitter end,it's not hard to label the protagonist as a mad
References: ¹ http://en.wikipedia.org/wiki/The_cask_of_amontillado - Baraban, Elena V. "The Motive for Murder in 'The Cask of Amontillado ' by Edgar Allan Poe." collected in Rocky Mountain E-Review of Language and Literature. Volume 58, Number 2. Fall 2004. ² http://en.wikipedia.org/wiki/Obsession_%28Spiritism%29 ³ http://www.afl.org.tr/mezun/e_bulten/2005/temmuz/leventmete.htm