In Shakespeare's 'Othello', Iago is a manipulative villain who strategically exploits the weaknesses of other characters, namely Roderigo, Cassio, and Othello, to orchestrate their downfall. He uses Roderigo's naiveté, Cassio's trusting nature, and Othello's insecurities to create chaos and convince them to act against their own interests. Ultimately, Iago's deceit leads to significant tragic consequences for all involved, showcasing his cunning and ruthless character.