I follow him to serve my turn upon him. (1.1.)

Iago says this line to Roderigo at the start of the play as he explains that he secretly hates Othello and is plotting against him. Although everyone, including Othello, believes that Iago is a loyal and devoted friend, Iago understands the strategic advantage that false friendship gives him. As a trusted confidante, he is able to sway Othello’s opinion and manipulate him much more effectively. The quote shows that from the moment the action begins, Iago is already looking for ways to bring about Othello’s downfall.

If thou canst cuckold him, thou dost thyself a pleasure, me a sport. (1.3.)

Here Iago explains how Roderigo can help him. He knows that Roderigo lusts after Desdemona and is angry to learn that she is married Othello. Iago encourages Roderigo to believe that by participating in Iago’s plot, he might have the chance to have an affair with Desdemona.

It is thought abroad that ‘twixt my sheets
He’s done my office. (1.3.)

This quote is one of the few moments where Iago explains his possible motivation for being obsessed with destroying Othello. He claims that there are rumors Othello has had an affair with Emilia, which would be a plausible reason for wanting to destroy Othello’s trust in his own wife. However, Iago only mentions this motivation very briefly, and it does not seem to fully explain the depth of his hatred toward Othello.

She did deceive her father, marrying you. (3.3.)

Iago makes this comment to Othello as a way of refuting Othello’s insistence that Desdemona is honest and would not lie to him. He points out that Desdemona demonstrably has the capacity to lie and keep secrets since she hid her courtship with Othello from her disapproving father. This quote shows Iago’s skill at psychological manipulation: he subtly plants a seed of doubt in Othello’s mind, using the couple’s own love as a weapon to increase the distrust between them.

Strangle her in bed, even the bed she hath contaminated. (4.1.)

Here Iago orchestrates even the way in which Desdemona will be killed. The quote shows Iago’s desire to control every aspect of how his plan will unfold, and also his sinister sense of poetic justice. He argues that since Desdemona has committed her crimes in bed, by sleeping with other men, she should also die in bed. The quote also reinforces the fact that Iago has complete control over Othello at this point, since Othello immediately agrees to the gruesome plan.