Iago is “two-faced” at almost every moment in the play. We see him lie outright to practically everyone in the play; in fact the only people who hear the unvarnished truth from Iago is the audience. The audience is in a very uncomfortable position: we see Iago, we hear him lie, and then he turns to us and conveys the simple truth – and then he turns back to the other characters and starts lying again. We see both of his faces at all times, though the characters don’t. Any audience member who shouted what she knows about Iago could stop the play in its tracks…but no one ever does. We are in a way complicit in his behavior, and almost admire his ingenious way of giving legitimately good advice to people in a way that still entraps them.
As far as an actor’s performance, one of the great traps of playing Iago is conveying too strongly how two-faced he is. If Iago seems obviously duplicitous, scheming and stroking his beard in the shadows, then all the other characters suddenly become stupid. An Iago who is obviously scheming and manipulative derails the play, because we wonder why anyone trusts someone so clearly slimy. Better to make Iago the most helpful, most kindhearted person on stage, and let the knowledge of what he really is be shared only with the audience and only when he’s otherwise alone. The mustache-twirling villain isn’t scary, but the best friend who literally stabs his buddy to death at a party sure is.
Iago managed to deceive each of the major characters at some point in the play.
Firstly, I would use Act II scene 3 where Iago dupes Cassio into drinking himself beyond sense. The actor playing Iago would be able to indicate to camera his contempt for Cassio’s confessed weakness-
…I have very poor and unhappy
brains for drinking. I could well wish courtesy would
invent some other custom of entertainment
As the carousing continues it would be possible for Iago’s duplicity to be demonstrated by the actor feigning intoxication for Cassio and the others, whilst showing how he is clearly in control to the audience as he engineers Cassio to his downfall.
As Cassio fights with Roderigo, Iago as catalyst for the battle could be portrayed in the ‘darkness’ of the scene – the audience may clearly see Iago provoking the action he then reports to Othello.