Who & Whom
From 'Grammar' part of The ABC Of Plain Words by Sir E Gowers (1951)

Who is the subjective case and whom the objective. The proper use of the two words should present no difficulty. But we are so unaccustomed to different case-formations in English that when we are confronted with them we are liable to lose our heads. In the matter of who and whom good writers have for centuries been perverse in refusing to do what the grammarians tell them. They will insist on writing sentences like "Who should I see there?" (Addison), "Ferdinand whom they suppose is drowned" (Shakespeare), "Whom say men that I am? " (Translators of the Bible). Now any schoolboy can see that, by the rules, who in the first quotation, being the object of see, ought to be whom, and that whom in the second and third quotations, being in the one the subject of is, and in the other the complement of am, ought to be who. What then is the ordinary man to believe? There are some who would have us do away with whom altogether, as nothing but a mischief-maker. That might be a useful way out. But then, as was asked in the correspondence columns of the Spectator by one who signed himself "A. Woodowl" (31 st December, 1948):

Regarding the suggested disuse of whom, may I ask by who a lead can be given? To who, to wit, of the "cultured" authorities can we appeal to boo whom and to boom who?

Whom will take some killing, too. Shakespeare and the Translators of the Bible have their distinguished followers today, such as Mr. Winston Churchill ("The slaves of the lamp . . . render faithful service to whomsoever holds the talisman"—Lord Randolph Churchill), Mr. E. M. Forster ("A creature whom we pretend is here already" — Spectator, 22nd November 1935) and Lord David Cecil ("West, whom he knew would never be seduced away from him" — Two Quiet Lives).§

But it has not yet become pedantic — at any rate in writing — to use who and whom in what grammarians would call the correct way, and the ordinary writer should so use them, ignoring these vagaries of the great. He should be specially careful about such sentences as:

The manager should select those officers who (not whom) he desires should sign on his behalf.
The manager should select those officers whom (not who) he authorises to sign on his behalf.
There has been some argument about who (not whom) should be authorised to sign on the manager's behalf.

See also Than.