Othello the Moor, a general employed by the Venetian state, has secretly married Desdemona, a daughter of the senator Brabantio. Iago, an ensign nursing resentment against Othello, enlists the help of Rodorigo, a disappointed suitor of Desdemona. They wake Brabantio in the middle of the night with the news of his daughter's elopement. Brabantio takes the case to the senate where, learning that she has married Othello of her own accord, he disowns his daughter. Othello is immediately ordered to the Venetian colony of Cyprus to repel a threatened Turkish invasion. Desdemona sails with her husband, taking with them her companion Emilia, who is also Iago's wife, and Othello's lieutenant Michael Cassio, newly promoted over Iago's head. Once in Cyprus, Iago plants the suspicion in Othello's mind that Desdemona has been unfaithful to him with Cassio. He engineers a drunken brawl for which Cassio is blamed and dismissed by Othello. Desdemona intercedes on Cassio's behalf but her constant pleas to Othello for his reinstatement only serve to convince Othello that Cassio is her lover. Iago acquires a treasured handkerchief that belonged to Desdemona and uses it as 'proof of the affair. Increasingly maddened by jealousy, Othello orders Iago to kill Cassio and strangles Desdemona himself. Emilia discloses her husband's plot and Othello, tormented by grief and remorse, kills himself. Iago, after murdering his own wife, is left to the justice of the Venetian state.
The lies and misplaced trust between Othello and Iago probably reflect the relationship between de Vere and Rowland Yorke.
In 1569, Yorke had fought with the Catholic rebels in the Northern Uprising. By 1572, Lieutenant (a rank Iago aspired to) Yorke he was fighting for the Protestant forces in the Dutch wars of independence. He was characterized as "a man of loose and dissolute behaviour and desperately audacious". Yorke had banned de Vere's wife - Anne Cecil - from de Vere's private chamber in 1573. In 1576, when de Vere returned from his foreign travels in a rage over the alleged infidelity of his wife, he stayed with Rowland and Edward Yorke. Edward Yorke was a servant of the Earl of Leicester - a rival of both the Cecil family and de Vere. By 1584, the libeler Charles Arundell accused the Earl of Leicester of various crimes, including attempting to disrupt the marriage of de Vere and Anne Cecil. If this accusation is true, Leicester was certainly successful. By 1584, in the Lowlands Yorke attempted to betray allied positions to the Spanish, and two years later, he did so again for silver. He died in 1588 reportedly from poisoning.
Yorke introduced into England a bold and dangerous way of thrusting the rapier in dueling. Iago brags that he had often "yerk'd ... [opponents] under the ribs."
Having visited Florence, he knew that its citizens were recognized for their arithmetic and book-keeping. The play notes this.
In the play, Philip Sidney provides the basis of the character of Michael Cassio.
The character Iago is probably named after the patron saint of Spain - Santiago.