He’s jealous of Cassio because got promoted to lieutenant over him even though he has never been in battle as he states in the play “One Michael Cassio, a Florentine (A fellow almost damned in a fair wife)That never set a squadron in the field,Nor the division of a battle knowsMore than a spinster—unless the bookish theoric,”(1.1.21-25) He is also jealous of Othello for many reasons including being married Desdemona, because Othello is black and has power and acceptance whereas Iago is white but has no power, he gave the position of lieutenant to Cassio and the fact that he thinks Othello slept with his wife. Iago admits “I hate the Moor: And it is thought abroad, that 'twixt my sheets He has done my office: I know not if 't be true; But I, for mere suspicion in that kind, Will do as if for surety.”
He’s jealous of Cassio because got promoted to lieutenant over him even though he has never been in battle as he states in the play “One Michael Cassio, a Florentine (A fellow almost damned in a fair wife)That never set a squadron in the field,Nor the division of a battle knowsMore than a spinster—unless the bookish theoric,”(1.1.21-25) He is also jealous of Othello for many reasons including being married Desdemona, because Othello is black and has power and acceptance whereas Iago is white but has no power, he gave the position of lieutenant to Cassio and the fact that he thinks Othello slept with his wife. Iago admits “I hate the Moor: And it is thought abroad, that 'twixt my sheets He has done my office: I know not if 't be true; But I, for mere suspicion in that kind, Will do as if for surety.”