Iago is such a terrifying character because he revels in what he is doing. The motivating reasons can be analysed: broken pride; a sense of betrayal; jealousy; ambition; desire for power over others; or even unrequited love turned sour, if you want to read it that way. It’s true that villains often fool themselves into believing their actions are justified or the fault of fate or caused by others; but the main factor with Iago is the huge elephant in the room. Iago knows he is the villain and sadistically enjoys the suffering he causes. His motivation is the full embracing of enmity.
