Iago hates Othello as he says in his soliloquy (Act 1 Scene 3). He suspects that Othello has slept with his wife and makes a plot to destroy him. Iago is also jealous of Othello because Othello just promoted Cassio who Iago thinks is a "pretty boy". He tells this to the audience as Shakespeare is using dramatic irony to engage the audience, as Iago is jealous himself, and he is trying to make Othello jealous. The thought that Othello has slept with his wife eats him "Like a poisonous mineral that gnaws my innards". Shakespeare is using dramatic irony predicting the tragedy that will follow. "Othello may be convinced. Desdemona's virtue will be blackened, turned into a pitch".
Othello originally came from Africa and he is one of a few in Venice who is a foreigner. So he's called things such as "thick lips", "black ram", "Barbary horse" and "devil" but Despite this he is married to the beautiful Desdemona who Othello thinks only married him because he told her interesting stories from where he came from and felt sorry for him. Othello becomes scared she might run off with someone else. He feels insecure about himself because he is a foreigner and this weakness is later exploited by Iago.
Othello's breakdown is mirrored in his language. His authority is summed up in a response to a challenge saying "Keep up your bright swords for the dew will rust them", meaning he will obviously defeat them and leave the swords lying so they will rust. This shows his arrogance and confidence in the beginning of the play because he assumes he will win every battle because after all he is a general.
When Desdemona's father, Brabantio accuses Othello of stealing Desdemona, Othello answers the charge with eloquent and subtle language. "Rude am I", when clearly he is not and he says he has no skill in the...