His goals changes during the play, however his motives are the same. Iago’s play evolves during the story, as he has to improvise because everything does not work out the way he had planned it to do; Cassio does not get killed and Rodrigo gets hurt, therefore Iago has to kill Rodrigo to ensure that Rodrigo can not rattle on him. In addition, his wife (Emilia) rattles on him when she hears the truth about him. Subsequently, he kills Emilia, which was not originally a part of his plan. In addition, Iago’s plan appears to succeed when Othello kills Desdemona, who is innocent of Iago's charges. But shortly afterwards Iago’s treachery is brought to light by Emilia. As a result of this, Iago kills his Emilia, which was not originally a part of his plan. And subsequently, Iago is placed under arrest. He remains famously reticent when he gets pressed for an explanation of his malicious conduct:
“Demand me nothing. What you know, you know.
From this time forth I never will speak word” [Act 5, Scene 2, Line 300-301].