pronoun

1. what or which person or persons: used to introduce a direct, indirect, or implied question who is he? I asked who he was; I don't know who he is
2. the person or persons that, or a person that: used to introduce a relative clause the man who came to dinner
3. any person or persons that; whoever: used as an indefinite relative with an implied antecedent “who steals my purse steals trash”

Etymology: ME who, ho, hwo < OE hwa, masc. & fem., hwæt, neut., who? what? (akin to L qui): for IE base see what