Iago hates Othello and devises a plan to destroy him by making him believe that Desdemona is having an affair with his lieutenant, Michael Cassio.

At the beginning of the play, Iago claims to have been unfairly passed over for promotion to the rank of Othello's lieutenant in favour of Michael Cassio.

Iago is one of Shakespeare's most sinister villains, often considered such because of the unique trust that Othello places in him, which he betrays while maintaining his reputation for honesty and dedication.

Fred West contends that Shakespeare was not content with simply portraying another "stock" morality figure, and that he, like many dramatists, was particularly interested in the workings of the human mind.

[6] The same critic also famously said that "to compare Iago with the Satan of Paradise Lost seems almost absurd, so immensely does Shakespeare's man exceed Milton's Fiend in evil".

[6] Weston Babcock, however, would have readers see Iago as a "human being, shrewdly intelligent, suffering from and striking against a constant fear of social snobbery".

[8] John Draper, on the other hand, postulates that Iago is simply "an opportunist who cleverly grasps occasion" (726),[9] spurred on by "the keenest of professional and personal motives".

[9] Following this logic, Draper concludes that Iago "is neither as clever nor as wicked as some would think; and the problem of his character largely resolves itself into the question: was he justified in embarking upon the initial stages of his revenge?

[10] This reading would seem to suggest that Iago, much like Don John in Much Ado About Nothing or Aaron in Titus Andronicus, wreaks havoc on the other characters' lives for no ulterior purpose.

He also enunciates in the aria that he believes an honest man to be a mocking actor about whom everything is a lie and that mankind is simply a joke of iniquitous fate.