A fool thinks himself to be wise, but a wise man knows himself to be a fool. Here 'himself' is a/an -

Reflexive pronouns end in -self or -selves. They refer back to the subject forms of personal pronouns.
Reflexive pronouns are:
- myself,
- yourself,
- himself,
- herself,
- itself,
- oneself,
- ourselves,
- yourselves,
- themselves.

Source: dictionary.cambridge.org