Itself is a reflexive pronoun, being the reflexive form of it. It can be used especially in the following ways:
as an object that refers to the same thing that is the subject of the sentence or that was mentioned earlier in the sentence: The machine switches itself off when it has finished printing. ♦ The civil war divided the country against itself.
after a singular noun or pronoun for emphasis: The document itself is divided into three parts. ♦ That itself is the problem.