pronoun; possessive whose; objective whom.
Origin of who
In most speech and writing, however, since who or whom often occurs at the beginning of the sentence or clause, there is a strong tendency to choose who no matter what its function. Even in edited prose, who occurs at least ten times as often as whom, regardless of grammatical function. Only when it directly follows a preposition is whom more likely to occur than who : Mr. Erickson is the man to whom you should address your request.
In natural informal speech, whom is quite rare. Who were you speaking to? is far more likely to occur than the “correct” To whom were you speaking? or Whom were you speaking to? However, the notion that whom is somehow more “correct” or elegant than who leads some speakers to make an inappropriate hypercorrection: Whom are you? The person whom is in charge has left the office. See also than.
Word Origin for who
Old English hwa, from Proto-Germanic *khwas, *khwes, *khwo (cf. Old Saxon hwe, Danish hvo, Swedish vem, Old Frisian hwa, Dutch wie, Old High German hwer, German wer, Gothic hvo (fem.) "who"), from PIE *kwo- (cf. Sanskrit kah "who, which;" Avestan ko, Hittite kuish "who;" Latin quis/quid "in what respect, to what extent; how, why," qua "where, which way," qui/quae/quod "who, which;" Lithuanian kas "who;" Old Church Slavonic kuto, Russian kto "who;" Old Irish ce, Welsh pwy "who").