Hatred is supposed to have a cause, some concrete event or insult that inspires a lasting rage. But in Othello, the play's villain is motivated by a hatred that seems to elude any reasonable definition. Iago's hatred and his determination to destroy his boss, Othello, seems out of proportion with the reasons he gives for it: anger that Othello did not promote him or jealousy that Othello might have slept with Iago's wife. Iago's loathing has been famously called a "motiveless malignancy" that redefines our understanding of hatred, making it seem a self-propelling passion rather than the consequence of any particular action.
In Othello, love and hate are shown to be two sides of the same emotion.
Iago is a force that converts everything into its opposite – above all, love becomes hate.
Just as Iago transforms Othello's love into hatred, the play subtly suggests that Iago's hatred for Othello is actually suppressed love.