誰/谁 (shuí) is the standard question word for who in Mandarin. It can function as a subject (谁来了?, who came?), object (你认识谁?, who do you know?), or modifier (谁的书?, whose book?). In rhetorical or universal quantifier uses, 谁都 or 谁也 means everyone or nobody depending on whether the verb is positive or negative: 谁都知道 (everyone knows), 谁都不知道 (nobody knows).