He is immoral in the sense of doing things in a different way against tradition almost, but is not immoral in the sense of going against other people’s ethics, although I suppose it depends on your viewpoint.
The reason being that Iago hates Othello so much is that he has chosen another man, Cassio, as his lieutenant, preferring him to Iago. This resentment, accompanied by Iago's cleverly fabricated accusations of adultery and his racism, cause Iago to despise Othello, and shortly thereafter, begin to conspire against him. Instead of simply killing Othello, Iago proceeds to attack him emotionally, which shows how Iago is quite human – he knows what will cause more damage to Othello in the long run, and instead of taking the easy option, Iago goes for the harder of the two options to get maximum benefits to himself. Iago begins to manipulate the people around him in order to hurt Othello and make him think that his wife, Desdimona, and Cassio are having an affair.
Iago makes clear right from the start his reasons for manipulating everyone. In soliloquy, Iago admits, "I hate the Moor."(Act 1, Scene 3, line 380). This line makes no attempt to justify his feelings, since true evil does not need real reasons, just rationalizations. For the first time Iago freely admits that all his evil is based around his simple hatred for Othello’s very existence.
One of Shakespeare’s other manipulative characters, Richard III, has a very evil and manipulating streak in him. Whilst being manipulative, he is very different to Iago. Richard has a hunger for power, and is willing to do virtually anything for it. Iago, whilst using people to get what he wants, he does not have the same desperate hunger for power. He wants to be The Moor’s lieutenant, but does not want to take over the role of Othello. Richard wants to be the ruler of the kingdom, and just brushes anything that stands in his way aside, be it his brother or a stranger.
It quickly becomes apparent, that Richard simply uses his deformity as a tool to gain the sympathy of others—including the readers. Richard's evil is a much more innate part of his character than simple bitterness about his ugly body. Iago does not repeatedly use anything to get sympathy from the audience. He doesn’t seem even particularly bothered about how he is portrayed to the audience and others, just so long as the people who matter don’t find out. So in some ways Iago is a simpler character than Richard, because right from the start we can see that Iago is a nasty piece of work, and he doesn’t cover it up with charisma like Richard does.
Once Richard stops exerting his charisma on the audience, his real nature becomes much more apparent, and by the end of the play he can be seen for the monster that he is. You could say that he gets what he deserves at the Battle of Bosworth. Perhaps the only thing that we see in the play that shows that Richard is human is the dream that he has before the battle, in which the ghosts of all the people he has murdered appear and curse him, telling him that he will die the next day. This could be taken as proof of Richard’s guilty conscience showing through.
Richard is clearly a villain - he declares outright in his very first speech that he intends to stop at nothing to achieve his evil designs. Iago is a lot more human than Richard – he shows feelings at times, especially towards the end of the play, and can make mistakes in the heat of the minute. A good example of this is in Act 5 scene 2, right at the end of the play, when Emilia starts to piece everything together. He tries to shut her up by saying on line 218 when he says, “Zounds, hold your peace!” but this, if anything just spurs her on more. Then, on line 222 everything falls apart around Iago because he realises how he has underestimated his own wife, and promptly draws his sword on her. This again, spurs her on and she starts stringing everything together out loud, and everyone then starts to realise how manipulating Iago has been.
Iago and Richard are both very good talkers, and can influence people just by simply using their tongues. There have been other famous villains that have had the gift of being a great speaker, namely Adolph Hitler and many of his henchmen. Having the gift of being able to talk well is obviously a major asset to all villains, and Richard certainly made the best use of his skills. Even characters such as Lady Anne, who had an explicit knowledge of Richard’s wickedness, allow themselves to be seduced by his brilliant wordplay, his skilful arguments and his relentless pursuit of his selfish desires.
For the most part of the play, manipulating people works perfectly well for Iago, and nobody realises what he is doing behind his or her backs. This, I think, is the main reason why Iago can be classed as a villain, and not as just someone in the background who influences the outcome.
Iago has many reasons for acting the way he does, his reasons may not be right or logical but he believes in them so strongly that he is willing to kill and destroy peoples lives in the process of completing them. His entire motives stem from one thing, jealousy. All of Iago’s motives are due to this single feeling. His revenge comes from wanting to avenge the people he is jealous of. He seems to elaborate on these initial ideas until he thinks that everybody has slept with his wife, for this he wants further revenge.
At first glance, Iago seems to have no motive for the destruction he is causing. However, despite Iago's unquestionable growth, the motivation behind his actions lie more in Iago's quest for personal gain, as opposed to just being evil for evil's sake. In order to achieve his personal gain Iago manipulates Rodrigo, Cassio and, most importantly, Othello.
So in conclusion, I think that Iago is definitely a very human villain, as he is evil, but is not as perfect or as evil as other Shakespeare characters. He shows deep emotions at times, and it is clear from the start that he is aware about what he is doing and he thinks that he is right in doing the things that he does.
