What is what part of speech is themselves?

Themselves is a pronoun. Specifically, it is a reflexive pronoun, which is used when the subject and object of a sentence refer to the same person or thing. Themselves is the reflexive form of the pronoun they, and is used to show that the action of the verb is being done by the same group of people or things that is being affected by it. For example, in the sentence "They made themselves breakfast," themselves acts as the direct object of the verb made, and refers back to the subject they.