Final answer:
It is Iago who informs Othello about the instigator of the brawl in Cyprus, though his account is manipulative and aimed at discrediting Cassio.
Step-by-step explanation:
When Othello asks who started the brawl in Cyprus, it is Iago who finally tells him the truth, albeit in a deceptive manner. Although Iago is the instigator of much of the drama within the play, he presents himself as reluctant to accuse others and fabricates a story that places Cassio in a bad light, ultimately leading to Cassio's dismissal from his position. Iago's manipulative actions serve as a catalyst for the tragic events that unfold in Shakespeare's play.