Treachery
The main theme of the film is treachery, chiefly, the betrayal by Iago of his "master" and friend Othello on both a professional and a personal level. Othello considers Iago a loyal lieutenant and has no idea that Iago actually hates him because he is jealous of his life and success, as well as his financial prosperity. Iago wants this for himself and so displays a Machiavellian nature when he comes up with a play to trick Othello into believing that his wife and his ensign are having an affair. He is the consummate con-man and it is his subterfuge and treachery that form the central plot of the movie.
Infidelity
Infidelity is a secondary theme in the film, which is ironic, because unlike most Shakespeare plays and adaptations, Othello contains no actual infidelity, but instead revolves around the rumors about and the suspicion of an extra marital affair. It is his distress and anger of his wife's supposed infidelity that disturbs the balance of Othello's mind and causes him to kill his wife, and it is the realization that infidelity has not taken place that drives him to kill himself. The theme also explores the way in which the planting of a seed of suspicion of infidelity can spiral out of control and can be enough for a jealous person to hang their hat on, without any actual evidence to prove that infidelity has occurred at all.
Tragedy
The play, and therefore the adaptation, is considered to be a tragedy, but tragedy is also one of the themes. Othello is a deeply tragic character; he is so in love with his wife that the thought of her betraying him makes him almost mad. He is also so angry about the perceived infidelity that he kills her. This is in of itself a tragedy, but on realizing what he has done, he also kills himself, another tragedy, because two upstanding, brave and loving characters end up dead because of a plot based on a jealous lie.
