Cassio functions mainly to move the plot forward by inadvertently becoming a pawn in Iago’s plan. Cassio’s thoughts, feelings, and motivations are rarely revealed, but his character and behavior are significant for creating the conditions under which Iago can enact his plan. Cassio is handsome, charming, and charismatic; as Iago notes when he starts to hatch his devious plan, “He hath a person and a smooth dispose / To be suspected, framed to make women false” (1.3.). If Cassio was not a potentially appealing lover, the idea that Desdemona was having an affair with him would be much less plausible, and Iago’s plan would be harder to pull off. In addition to his innate appeal, Cassio’s behavior to women unwittingly endangers both himself and Desdemona. He often performs shows of gallantry and courtesy which are open to misinterpretation as flirtation. Watching Cassio touch Desdemona’s hand, Iago schemes that “Ay, smile upon her, do! I will gyve thee in thine own courtship” (2.1.).
Cassio’s behavior is rooted in a deep sense of honor: when Iago tries to get him to say lewd things about Desdemona, he insists on being respectful, observing “An inviting eye—and yet methinks right modest” (2.3.). Cassio is also horrified when his drunken behavior results in public shame, lamenting “Oh, I have lost my reputation!” (2.3.). Perhaps because Cassio is a Florentine, and not a Venetian, or because he seems to lack the military experience of some of the other male characters, he is rather naïve and trusting. Cassio’s innocence and trust that other people will see his virtue makes him a parallel character to Desdemona. However, unlike Desdemona, Cassio evolves as a character. By the end of the play, he has realized that Iago is responsible for Desdemona’s death, and he helps Othello understand Iago’s treachery. Cassio ends the play in a position of significant authority and responsibility: Ludovico commands that “Cassio rules in Cyprus” (5.2.) and entrusts him with punishing Iago. The impact of the shocking betrayals and violence shown by other characters has presumably changed Cassio into a man who will be much more cautious, but possibly a better leader as a result.