Themself
Themself is a reflexive pronoun used with the singular they to refer back to a single person whose gender is unknown or nonbinary. It is formed to parallel other reflexive forms such as himself, herself, and themselves, using they as the antecedent.
Usage notes: In most contexts, “themselves” remains the common reflexive form for singular they: They bought
History and variation: The singular they has a long history in English. The traditional reflexive form for
Usage considerations: For formal or traditional contexts, many editors still default to themselves for singular they,