Jealousy is the driving force behind this play. Without it, there would be no play. Iago's entire plan for revenge against Othello revolves around Othello's jealousy.
The way Iago does this is through planting little seeds of doubt about Othello's wife Desdemona in Othello's mind as the play progresses. He does it gradually, though, instead of bombarding him with accusations against Desdemona. Iago involves quite a few characters in his evil plot, including Emilia, Roderigo, Cassio, Desdemona, Brabantio, along with others.
Othello's jealousy, once he is convinced Desdemona has been unfaithful to him, drives him to madness and murder. He kills Desdemona and destroys other lives along the way. Others, like Emilia and Roderigo, also lose their lives in this evil plan of Iago's.
For more information, see this eNotes link: http://www.enotes.com/othello/themes