Cunning, clever, and dishonest, Iachimo is a force to be reckoned with. He easily finds Posthumus's weakness (his secret fear about his wife's faithfulness) and exploits it for all it's worth. How long does it take Iachimo to get Posthumus to agree to a lose-lose bet? About five minutes. Everyone can see what a bad deal it is for Posthumus... except Posthumus himself.
Hmm… where have we seen this kind of thing before? With Shakespeare's master villain, Iago, that's where. Yep, the slimy, sociopathic con artist in Othello also fools a man into believing his wife's cheated on him—only (spoiler alert!) her death isn't fake. In fact, "Iachimo" pretty much means "little Iago."
So why is there this big connection to Shakespeare's evil genius?
Well, for one thing, it's entertaining. We tend to think of evil people as brutal and insensitive, or at least disconnected from the people they hurt. Iago and Iachimo, however, are able to hurt Othello and Posthumus so much because they understand them so well: they get inside the heads of the people they're trying to hurt.
And we hate to say it, but we get kind of interested in seeing how it all unfolds. It's not that we want Iago and Iachimo to win, exactly, but we do want to see where it all takes Posthumus and how it all plays out.
Maybe Shakespeare wanted to take another crack at Iago, but with a twist. Unlike Iago, Iachimo apologizes for what he's done at the end of the play. He tells Posthumus his "heavy conscience sinks" him (5.5.504). He seems to feel bad for what he's done… when he's finally caught, that is; we can't help but notice that Iachimo is forced into telling his tale. But unlike Iago, he actually complies.
Iachimo, then, is kind of a stripped-down version of Iago. Because he's not quite as nasty as Iago, all the trouble in Cymbeline gets resolved without any of the good characters buying the farm. But maybe Shakespeare is saying something else, too: Iachimo is a smart, trendy, popular guy at the Roman court, just doing what smart, trendy, popular guys at the Roman court do. The fact that he has so much in common with Iago may show us that there's something insidious—even evil—about these suave guys involved in politics and power.
Iachimo may look like a lesser version of Iago, but he can do just as much damage.
If you don't like that theory, how about this: Iachimo has fun being evil. The same way that some people enjoy writing songs or filming movies, Iachimo seems to enjoy making bets that might ruin people's lives. He does it with a sense of craftsmanship, appreciating the elegance or cleverness of a particular step in his scheme as much as its final result: incredible suffering for the people he has chosen.
His sexualized language, puns, and jokes about women are all fun and games. Until they aren't.
Iachimo might start out making fun of how much men value their own women, but it quickly turns serious when he actually gets to Britain. Once Imogen flat-out refuses him, Iachimo decides that instead of losing a bet, he'll cheat to win. Sounds like a plan, right?
Wrong. His little scheme involves hiding in Imogen's room and taking a peak at what's under her nightgown. His little excursion to her room without an invite is like a symbolic rape: he steals her most prized possession (bracelet) and even gets an eye full of things that should be private.
Even though Iachimo comes clean in the end, he's got a lot to answer for.