Iago agrees to help Roderigo to find an approach to Desdemona. However, he never fulfills his promises, betraying him instead. Iago uses Roderigo to destroy Cassio’s reputation and career. Besides, the villain takes the jewelry from naive Rogerio but doesn’t give it to Desdemona. He manipulates Rogerio to satisfy his plan and enrich himself.
Detailed answer:
The readers see Iago manipulating Roderigo multiple times in the play. Still, Iago’s villainy reaches its peak in Scene 2 of Act 4.
Rogerio starts suspecting Iago in his dishonesty. Tired of waiting for a response from Desdemona, Rogerio rages at Iago:
Every day thou daffest me with some device, Iago;
and rather, as it seems to me now, keepest from me
all conveniency than suppliest me with the least
advantage of hope. I will indeed no longer endure
it, nor am I yet persuaded to put up in peace what
already I have foolishly suffered.
(Act 4, Scene 2)
He is curious why Desdemona ignores him, unaware of Iago’s sneaky deeds. He doesn’t know that Iago never gave his expensive presents to Desdemona:
The jewels you have had from me to
deliver to Desdemona would half have corrupted a
votarist: you have told me she hath received them
and returned me expectations and comforts of sudden
respect and acquaintance, but I find none.
(Act 4, Scene 2)
Thinking of personal enrichment, the villain takes the jewels himself.
Nevertheless, Iago manages to convince him to follow the initial plan. In Act 2, he made Roderigo challenge and fight drunk Cassio. Now he decides to kill the man, getting rid of a personal enemy.
Iago convinces Roderigo to murder his rival when he ensures Cassio is the next candidate for Desdemona’s heart. By killing him, Rogerio’s chance to marry Desdemona increases:
O, no; he goes into Mauritania and takes away with
him the fair Desdemona, unless his abode be
lingered here by some accident: wherein none can be
so determinate as the removing of Cassio.
(Act 4, Scene 2)
Evident from the text, Iago manipulates Rodrigo by lying. He states that they want to withdraw Othello from Cyprus, handing over the governorship to Cassio. The Moor will take Desdemona with him from here. The only chance to avoid this is to kill Cassio. Thus, Rodrigo decides on this crime as Iago promises to help him.
Iago’s plan in Act 4 turns out to be fatal for Desdemona and destructive for Rogerio.
Being manipulated by Iago, the man makes a bold attempt to kill Cassio according to the plan. As he says:
I have no great devotion to the deed;
And yet he hath given me satisfying reasons:
‘Tis but a man gone. Forth, my sword: he dies.
(Act 5, Scene 1)
In the process, Iago becomes the one who murders Roderigo and inflicts major wounds on Cassio. Only then Roderigo realizes that Iago used him and exclaims:
O damn’d Iago! O inhuman dog!
(Act 5, Scene 1)
When the public arrives, Iago manipulates the crowd. He shifts the blame and suspicion towards Bianca.
Rogerio becomes a victim of Iago’s manipulation. To get rid of the potential enemy, Iago kills him at the very first opportunity. Iago’s personal plan is highly adjustable. His actions are heavily reliant on the outcome of the fight. He always seeks to find the most suitable position in the ever-changing dynamics of the surrounding people.