Iago is consumed by jealousy of Cassio.

Iago was jealous of Cassio's promotion and wished to rid himself of the man regardless of what it took to do so. He plans to solve the problem by ruining Cassio's reputation and ultimately wishes for him to lose his life. In the end, Cassio regains his honor and takes over as the troops temporary leader in Cypress. He also has Iago arrested for his crimes.