'谁也不' is a compound pronoun meaning 'nobody' or 'not anyone'. It combines the interrogative pronoun 谁 ('who'), the emphatic particle 也 ('also, even'), and the negator 不 ('not'). Together, they form a strong negative universal quantifier—literally 'not even who', i.e., no person at all. It functions as a subject or object and always appears before a verb, never alone.

This expression is common in spoken and written Mandarin to stress complete absence of people involved in an action. It carries a tone of universality and finality—more emphatic than just 没人. It’s frequently used in contexts involving inability, refusal, knowledge, or participation (e.g., 'nobody knows', 'nobody agrees'). Unlike English 'nobody', 谁也不 must be followed directly by a verb or adjective; it cannot stand alone as a noun phrase without a predicate.