What sort of person is Cassio? In Act II, what happens to him, and how does Iago plan to use the situation in his plan against Othello?

One of the interesting things about the character of
Cassio is that Shakespeare reveals it to us through the way others see him, almost as if
he is just a reflection of what people want him to be. Iago's impression of him is the
first one we get, but Iago sees him through eyes clouded by jealousy. Cassio has gotten
the promotion Iago thinks should be his, so he is scornful of Cassio's ability. He sees
Cassio as a brown-noser and not a real soldier. Cassio is an outsider and a newcomer. To
Desdemona, Cassio is a loyal friend; to Othello he is a fine choice for
Lieutenant.

Iago sets up Cassio to get into a drunken sword
fight with his henchman Roderigo, hoping to get him killed. When Roderigo proves too
cowardly to kill Cassio, Iago uses the opportunity to get Cassi demoted and then puts
the idea into Othello's head that Cassio is having an affair with Desdemona. Cassio
appears to be oblivious to all of this plotting throughout the entire play and is as
surprised as everyone else when he finds out the truth about Iago. Cassio is a linchpin
to Iago's plans, but he is not important in and of himself.