Iago is such a transfixing portrait of evil exactly because his motives are forever murky.
In 2009, he played Iago, opposite John Ortiz as Othello, at the Skirball Center for the Performing Arts.
JI: There is a sort of Iago—someone who is up to some real trouble making—in the book.
For instance, Iago declares in Othello that, “Good wine is a good familiar creature, if it be well used.”
Iago feels the necessity of obtaining motives for his conduct.
Iago resolves to make use of Desdemona to cause Cassio's downfall.
But the alliance of evil like Iago's with supreme intellect is an impossible fiction; and Shakespeare's fictions were truth.
Edmund, the tribunes, Iago, and (in this play) Octavius Cæsar are such souls.
This is exactly Iago with Othello—believing in virtue, using, despising it.
Could we speak as favourably of his Iago, we should have introduced him in the proper place.