In Iago's soliloquy in Act 1 Scene 3, Iago exclaims 'I hate the Moor'; he repeats this sentence many times during the first act of the play. The reasons for his hatred are vast, they could stem from racism, for Iago uses derogatory terms to describe Othello many times, Barbary horse', devil' and old black ram'. It could also come from Iago's resentment that Cassio was promoted above him by Othello. One of the main reasons is that it is rumored that Othello has slept with his wife Emilia,
"And it is thought abroad, that 'twixt my sheets he has done my office". Iago's jealousy of Othello can be argued to be the main motive for all his evil actions for he mentions it again in the following soliloquy,
"For that I do suspect the lusty Moor hath leap'd into my seat". Iago is dead-set on thinking that his wife is having an affair and it would explain his choice of revenge making Othello believe that Desdemona is sleeping with Cassio for payback for him sleeping with his own wife. Of course, it is unlikely that Othello and Emilia actually had an affair, but Iago is so used to lying and deceiving that he assumes that everyone else must be doing it too, and therefore he becomes paranoid about even the slightest thing.
Iago says that Othello is too trusting in men, and that he will be able to be manipulated as easy as an ass is,
"The Moor is of a free and open nature that thinks men honest that but seem to be so, and will as tenderly be led by the nose as asses are." Iago is portraying Othello as a fool, but it might be Iago's jealousy clouding his judgment. Iago firmly believes that he will be able to manipulate Othello into believing