I must add a third one: he is the utterly heroic figure, the only character that actually fights the causality of the programming philosophy of the matrix. He seems to defend causality in his statements, but in fact he fights it. Just as Neo and the others argue to defend choice but whatever they do, they cannot escape the causality, even they prove it to be true, giving the matrix another turn for survival. Were it for Smith, he would just destroy everything, including himself, forcing the architect (or whoever is in charge of the matrix) to shut down the system, which could perhaps be a better idea.