In Othello, there is grotesque sexual and animalistic imagery, which is quite hideous. Iago says to Brabantio, regarding Othello and Desdemona's relationship:
I am one, sir, that comes to tell you your daughter
and the Moor are now making the beast with two backs.
Jealousy is personified as both hideous and a monster. Iago warns Othello:
O, beware, my lord, of jealousy;
It is the green-eyed monster which doth mock
The meat it feeds on;
Cassio says that if a man loses his reputation he becomes hideous and bestial:
Reputation, reputation, reputation! O, I have lost
my reputation! I have lost the immortal part of
myself, and what remains is bestial. My reputation,
Iago, my reputation!
Emilia uses hideous gastro-intestinal imagery to describe the way men treat women:
They are all but stomachs, and we all but food;
To eat us hungerly, and when they are full,
They belch us.
The word "hideous" is only used once in the play, used by Othello to refer to a monster that could mean both himself or Iago. It could also stand for jealousy (Othello) or deceit (Iago) personified.
By heaven, he echoes me,
As if there were some monster in his thought
Too hideous to be shown.
All in all, Iago is the most hideous character in the play. He is a sexist misogynist, the devil incarnate, an agent of chaos and destruction. He seems to revel in pain, even his own. And he wonderfully uses language as his primary weapon. When he is stabbed and all his injuries inflicted, he goes silent.