He knows that Roderigo can give him money in exchange for his schemes and friendship. Having seen the other person’s weakness, he maximizes on it for his own devious ends. In addition, he hates Othello for picking Cassio as his lieutenant (I.i. 7–32), so that he promises himself that he will not let this unfair treatment go unnoticed. He plans to take his revenge by telling Othello that Cassio is sleeping with Desdemona (I.iii.369–370) and proves it through the aid of his wife Emilia and his other innocent “subjects”.
In Act 2, Iago begins to suspect that Cassio has a hidden desire for Desdemona because he praises her and Iago finds it as a means to his advantage. Because he knows that Roderigo will do anything just to win Desdemona, he convinces him that if he kills Cassio then he will have Desdemona, and Iago will take Cassio’s place as Othello’s lieutenant. It appears that Iago has become so engrossed in his plans that his imaginations have been confused in his own mind to be reality. Having been motivated by the urgency of his desire for revenge, he boldly plans to tell Othello that Desdemona and Cassio are having an affair so that Othello will discharge Cassio and appoint him as replacement for Cassio as lieutenant (II.i.286).
Iago’s schemes spare nobody who comes against his plans. He even discredits Cassio to Montano who has high regard of Cassio’s abilities and character. So when Roderigo attacks Cassio, Montano is also wounded. Iago appears gentle to Roderigo as he comforts him after the fight, the latter being unaware that he is just being used to achieve Iago’s personal and vested interests. To make matters worst, he uses his wife to let Desdemona and Cassio meet so that the meeting will appear to be a proof of Desdemona’s infidelity to Othello (II.iii.310).
Act 3 shows that Iago uses and performs well as a good actor that Othello does not suspect his true intentions and feelings as he pretends shock