Can we ever know the truth about a person? Is it possible to know if someone is lying to us? How can we discover what lies behind the words someone tells us? Shakespeare was fascinated with these questions. Many of his most evil characters were thought by others in the play to be sincere and truthful. In Othello, this theme has its most potent and dramatic realization in the character of Iago.
Iago fools everyone in the play into believing he's honest. No one even suspects him of treachery, until the final act when Roderigo first realizes how badly he's been fooled. In short, Iago proves that evil intentions can be masked behind a facade of honesty. The theme emerges in other characters: Brabantio is deceived by Desdemona's reaction to Othello, assuming she fears him when she truly loves the Moor. Othello suspects that Desdemona is unfaithful, despite her innocent looks. Othello also feels he's being deceived by Cassio, whom he trusts and who appears loyal. Emilia's exterior suggests salty indifference, but she turns against her husband and dies in defense of Desdemona. Even Bianca, who is suspected of dishonesty, is ultimately seen as a sincere and caring woman. And Othello, considered a barbarian by many in the play, is gentle and noble until driven to near-madness by the cruel manipulations of his most trusted "friend."
The inability to judge true from false is a human dilemma that we have all faced. In Othello's case, the dilemma proves fatal. Shakespeare dramatizes the problem by showing the consequences of trusting someone whose mask of honesty is perfect, almost to the very last.