(in Shakespeare's Othello). Michael Cassio was a Florentine, and Othello's lieutenant. Iago made him drunk, and then set on Roderigo to quarrel with him. Cassio wounded Roderigo, and a brawl ensued, which offended Othello. Othello suspended Cassio, but Iago induced Desdemona to plead for his restoration. This interest in Cassio, being regarded by the Moor as a confirmation of Desdemona's illicit love, hinted at broadly by Iago, provoked the jealousy of Othello. After the death of the Moor, Cassio was appointed governor of Cyprus.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894