Michael Cassio is depicted as a handsome, capable Florentine soldier who is promoted to the position of lieutenant over the more experienced Iago. Iago resents Michael Cassio for his promotion and believes that he is significantly more qualified for the position of lieutenant. Iago mentions the Cassio only possesses knowledge from the books he has read and feels that his military theory is "Mere prattle without practice."
Despite Cassio's inexperience, he accepts the position with enthusiasm and is depicted as an extremely loyal, courteous gentleman. Michael Cassio demonstrates his morally upright and polite nature by worrying about Othello's safety, kissing Emilia as an introduction, and complimenting Desdemona.
Although Michael Cassio is presented as a well-intentioned gentleman and loyal subject, Shakespeare also presents him as an undisciplined drinker and a naive individual. Iago is quick to recognize Cassio's weakness and successfully gets him drunk. Cassio fails to realize that Iago will benefit from his demotion and puts his trust in him.
After becoming intoxicated, Cassio fights Roderigo, and Othello removes him from his esteemed position. Cassio then demonstrates his regret and shame by lamenting his reputation.
Iago also uses Cassio's good looks to influence Othello's insecurities by suggesting that Desdemona is romantically interested in him. Similar to Roderigo and Othello, Michael Cassio is unable to recognize Iago's deceitful, malevolent nature and becomes the victim of his malicious plot.