Roderigo is a rich, unintelligent guy who thinks that if he sends Desdemona enough expensive presents, she'll fall in love with him. He's hired Iago to be his wingman, but Iago basically uses him as a walking ATM.
Iago takes the jewelry Roderigo thinks he's giving to Desdemona and sells it for a profit. All Roderigo does in response is to fall for Iago's smooth talking again and again. In the end, Roderigo dies—stabbed in the back (appropriately enough) by his wingman Iago.