speaking of butchers

"Doubtless one leading reason why the world declines honouring us whalemen, is this: they think that, at best, our vocation amounts to a butchering sort of business; and that when actively engaged therein, we are surrounded by all manner of defilements. Butchers we are, that is true. But butchers, also, and butchers of the bloodiest badge have been all Martial Commanders whom the world invariably delights to honour."  (Moby-Dick Chapter 24)

After supper—The Hunter in the mouth of his tent reclines, with a pipe, upon a glossy bearskin;—before him, a desert expanse of grass and river;—his attention is apparently divided between the moon, suspended over the western hills; the flickering blaze of a small fire, and the curling smoke which he deliberately exhales. His friend stirs a toddy, reading with difficulty a crabbed manuscript. Loquitur. "When I saw you yesterday, beside your usual duties, acting as guide, surgeon,—(for you have effectually cured the snake-bitten horse)—as hunter, or as butcher"—  

"Say commissary!"

"I conceived hopes of you, that the poetic spirit was layed; and when at supper to-night you ate so heartily of the elk-steak, I little thought you had been indulging again in such pathetic"—

"Pshaw! it serves for a gilding to Life's bitter pill! The delicious supper should have mended your humour: for I stake my reputation on it— as 'guide, surgeon and hunter'"—

Imaginary Friend. "And butcher"—

—"That the flesh, cooked, as it was, with a little pork, cannot be distinguished from that of the fattest buffalo cow that ever surrendered tongue and marrow-bones to hungry hunter.

I. F. Bravo! I have hopes of you! Kill your meat with a good conscience, and daily labour and excitement over, solid indeed is the hunter's comfort! With grass and bear-skin bed, his toddy, aud his soothing pipe—the musical ripple of the river sparkling in the moonbeams— I mean"—

"Fairly caught! I little thought when I heard you abuse my pathos over the noble beast that had yielded his life to my sport, that mere creature comforts would thus inspire you! Dear critic, and lover of bathos! hast thou found poetry in a full stomach?" 
(January 1852; and Scenes and Adventures in the Army)

 Imaginary Friend is spelled out, in italics--so there's no doubt about what I. F. stands for.