Othello is a play about sexual jealousy and how one man can convince another man, who loves his wife, that she has been unfaithful to him when she hasn't. Shakespeare creates several interesting and artistically bold characters in the story. His hero, Othello, is noble but flawed, with a tragic flaw in his pride. 

This pride is not solely noble or military, but self-serving and self-regarding, leading him to believe his innocent wife has been unfaithful to him. This makes him a more interesting tragic hero, as he isn't a spotless hero with one major blind spot, but everyone else but himself.

Sherlock doesn't make Iago, the villain, someone whose motives we can understand. Instead, he goes out of his way to make Iago as inscrutable as possible. He puts into Iago's mouth several plausible motives for wreaking the confusion and chaos that causes Othello's downfall and Desdemona's death. In providing multiple motives, Iago emerges as "motiveless," as described by Coleridge. While we cannot be sure why he is doing what he is doing, this does not mean he is not driven by anything.

Shakespeare's Iago is a dangerous human with human attributes and intellect who derives great pleasure from causing harm to others. He is a convincing ensign to Othello, a loyal servant to the Moorish warrior, while plotting his downfall. 

Iago is a moral pyromaniac setting fire to all of reality, as Harold Goddard famously said. Othello is unlike many of Shakespeare's other great tragedies, as its plot could easily have been co-opted for a comedy rather than a tragedy. 

Iago's role in Othello is similar to that of the villainous Don John in "Much Ado about Nothing", where Don John aims to wreck the marriage between Claudio and Hero. However, in Much Ado, Hero's fidelity is proven and Don John's villainy is exposed, creating a comedy. 

Much of Othello proceeds like a comedy, but it takes a dark turn at the end when it becomes apparent that Othello will not be reconciled with Desdemona and that his deep-rooted sexual jealousy and suspicion are too deep to be wiped out. 

Critics have observed that Iago is the stage-manager, director, and dramatist all wrapped up in one, with writers like Dickens and George R. R. Martin often discussing the act of "killing off" their own characters for the amusement of others.