This thing of darkness
Prospero:
Mark but the badges of these men, my lords,
Then say if they be true. This misshapen knave—
His mother was a witch. . . .
These three have robb'd me, and this demi-devil—
For he's a bastard one—had plotted with them
To take my life. Two of these fellows you
Must know and own; this thing of darkness I
Acknowledge mine.
Caliban:
I shall be pinch'd to death.
The once and future Duke Prospero of Milan and his daughter are stranded on an island with the native "demi-devil" Caliban, the bastard son of a witch and a demon. Caliban is compelled into servitude, and Prospero keeps him in line by having the local spirits administer pinches when necessary.
In more recent days, Prospero and his spirits have shipwrecked his treacherous brother Antonio (now the duke) and other nemeses on the island. Toward the end of the play, after torturing them for four acts, he gives them a direct piece of his mind. In this scene, two drunks stumble in with Caliban, after Prospero has foiled their inept plot to seize the island. By their "badges" (emblems of their master), the men are identified as Antonio's lackeys, and Prospero dryly asks his brother whether his servants "be true" (are honest). But his contempt for them is more than matched by his disgust at his own rebellious slave, "this thing of darkness" which Prospero must "acknowledge mine."
Prospero's phrase recalls the way the clown Touchstone describes his rustic fiancée in the comedy As You Like It: "A poor virgin, sir, an ill-favor'd thing, sir, but mine own; a poor humor of mine, sir, to take that that no man else will" (Act 5, scene 4). Touchstone's "humanitarian" realism stands in marked contrast to Prospero's unforgiving vilification of the often sympathetic Caliban.