Iago is brilliant. It's simply said, but it's true. He embodies the perfect evil character: he's emotional but not rash, honest but not faithful, and, most importantly, clever. He is, indeed, a moral pyromaniac – moral only because he knows the lines between good and bad. One might say he actually ignites the lines between good and bad, burning them to the point where no one knows who fits where.
Almost immediately after the play begins, we can see that Iago will cause Othello's downfall. He begins his subtle war with Othello, and by his actions throughout the play, it's obvious that he is enjoying it. Thus, war has become a game. He illustrates his satisfaction with his evil during this passage: "How poor are they that have not patience! / What wound did ever heal but by degrees? / Thou know'st we work by wit, and not by witchcraft; / And wit depends on dilatory time. / Does't not go well? Cassio hath beaten thee. / And thou, by that small hurt, hast cashier'd Cassio: / Though other things grow fair against the sun, / Yet fruits that blossom first will first be ripe: / Content thyself awhile. By the mass, 'tis morning; / Pleasure and action make the hours seem short..." (Act 2, scene 3). The key word in this passage is "pleasure" – Iago is clearly enjoying watching his plan unfold. He is dominating the situation, and, like he would in war, he is reveling in his victory so far. And similar to how fun games can make time go by faster, watching Othello's life unravel is providing the same kind of thrilling rush for Iago.
Although Iago is quite the devil now, he wasn't always like that. We never see the loyal Iago, although we do see the loving Iago. Iago professes his love for Othello so often that it's hard to believe he really hates him so much. He often says lines similar to, "My lord, you know I love you." Prior to the beginning of the play, Iago must have been devoted to Othello – and because he stood in such good graces with Othello, he was able to deceive him and ultimately destroy him. This is why the play is so tragically ironic.
So Iago does take on the role of the moral pyromaniac, and he succeeds in blurring the lines between good and bad. Is Roderigo good because he had good (yet ignorant) intentions, or is he bad because he failed to recognize Iago's glaring evilness? Is Othello good because he did everything he did with justice and honor in mind, or is he bad because he acted so rashly? Although these questions aren't difficult to answer, Iago succeeded in setting fire to things so quickly that by the time the fire was put out, it had already burned everything to a crisp.
