Webster's Revised Unabridged Dictionary · 1913

Who

Who , pronoun

[Old English who, wha, Anglo-Saxon hwā, interrogative pron., neut. hwat; akin to OFries. hwa, neut. hwet, Old Saxon hwē, neut. hwat, Dutch wie, neut. wat, German wer, neut. was, Old High German wer, hwer, neut. waz, hwaz, Icelandic hvat, neut., Danish hvo, neut. hvad, Swedish ho, hvem, neut. hvad, Gothic hwas, fem. hwō, neut. hwa, Lithuanian kas, Ir. & Gael. co, Welsh pwy, Latin quod, neuter of qui, Greek po`teros whether, Sanskrit kas. r182. Compare How, Quantity, Quorum, Quote, Ubiquity, What, When, Where, Whether, Which, Whither, Whom, Why.]

1.
Originally, an interrogative pronoun, later, a relative pronoun also; -- used always substantively, and either as singular or plural. See the Note under What, pron., 1. As interrogative pronouns, who and whom ask the question: What or which person or persons? Who and whom, as relative pronouns (in the sense of that), are properly used of persons (corresponding to which, as applied to things), but are sometimes, less properly and now rarely, used of animals, plants, etc. Who and whom, as compound relatives, are also used especially of persons, meaning the person that; the persons that; the one that; whosoever.
Let who will be President. — Macaulay
[He] should not tell whose children they were. — Chaucer
There thou tell'st of kings, and who aspire; Who fall, who rise, who triumph, who do moan. — Daniel
Adders who with cloven tongues Do hiss into madness. — Shakespeare
Whom I could pity thus forlorn. — Milton
How hard is our fate, who serve in the state. — Addison
Who cheapens life, abates the fear of death. — Young
The brace of large greyhounds, who were the companions of his sports. — Sir W. Scott
2.
One; any; one. [Obsolete, except in the archaic phrase, as who should say.]
As who should say, it were a very dangerous matter if a man in any point should be found wiser than his forefathers were. — Robynson (More's Utopia)