Iago's importance to the play is revealed through the significance he has in determining the direction of the plot. Just like a masterful puppeteer, he has forcefully steered its' direction. Shakespeare, at the very beginning of the play does not bother to develop the character of the protagonist, Othello but rather places greater emphasis on plot development. We are immediately introduced to Roderigo and Iago and are privy to their conspiracy to undermine Othello. With a masterful stroke, Iago subdues Roderigo, his 'dupe' and sets up the initial plot- Iago intends to gain his rightful position of lieutenant by destroying Othello and Casio. "I Know my price, I am worth no worse a place." Although Iago's plan does not change throughout the play, his motives, which obviously influence his actions do. Iago's initial motive in destroying the protagonist is hatred. "I hate the Moor." This shifts to jealousy, "He's done my office", to just sheer malignant motives. "If Cassio do remain he hath a daily beauty in his life that makes me ugly." It is as if Iago has allowed us to follow his journey from revenge to finally madness.
Iago's emotive feelings are dictating the direction of the plot. The audience ponder whether Iago will gain some control and restore balance. By Act 3 sc. iii he has achieved half of his objectives. Cassio has been removed and Iago has replaced him as lieutenant. 'Now art thou my lieutenant'. Instead Iago, full of rage and satisfaction that is plan is working so well continues his destructive plan. All the while Iago's 'medicine' is working to 'put the Moor at least into a jealousy so strong that judgement cannot cure'. He so easily controls the 'levers' of the play.
The success of Iago can be attributed to his ruthless motivation fueled by his emotions. From the outset, Iago sets up his plan and motivations. With tenacity, he sticks to it. 'Dull not device by coldness and delay'. Even when flaws start to appear in his plan he still goes on with it. 'The moor may unfold me to him- there stand I in much peril'. This, in effect, undermines his own success- because he does not know when to stop, he cannot see his own destruction coming. Throughout the play the imagery of a spider drawing his net to catch his prey is constantly used. 'I Shall ensnare them all', Iago says. So just like a barbaric animal, Iago has set his web and nothing can stop him now.
Iago success is also achieved because he positions everything correctly. This involves getting Cassio drunk, arranging 'the' handkerchief to go missing in Cassio's quarters and personally beguiling Othello's mind into thinking Desdemona is cuckolding him. Obviously without these events (so remarkably planned by Iago), the plot would never have developed. With great skill, Iago is able to arrange a conversation between Cassio and Bianca and carefully position Othello so that he thinks Cassio is discussing his wife. 'Oh, dear Cassio! As it were. His gestures import it'.
However, Iago's success is partly due to luck. Luck that the handkerchief was dropped by Desdemona and retrieved by one of Iago's unsuspecting puppets, Emila. Luck that Cassio was confronted by...