Roderigo, Iago's pawn in Othello, is clearly an outsider in the main characters' society. At the start of the play, we learn that Desdemona and her father, Brabantio, have both decided that Roderigo would not be a suitable match for Desdemona. For the rest of the action of the play, Roderigo tries desperately to win Desdemona's love. But because he is such an outsider in Cyprus (that is, no one really knows him or acknowledges his presence), he is able to carry out Iago's dirty work. Iago views Roderigo as expendable, and since he doesn't exist in the main characters' inner circle, he ultimately--and unfortunately--is.
More importantly, Iago is an outsider of sorts--even though other characters view him as a trusted friend. Iago, as evidenced through his soliloquies, is unable to function as a member of the society in which he lives. His hatred for Othello, his willingness to destroy the lives of other characters to get back at Othello, and his over-inflated sense of self-importance make him the ultimate outsider.