archfiend

A chief fiend (devil, demon or monster).

Of those [spirits] who rebelled some became devils, fiends or archfiends, according to the manifold proportions of their transgression.

[…] he thought for a minute with a freezing detached almost amused calm of the dreadful night inevitably awaiting him whether he drank much more or not, his room shaking with daemonic orchestras […] the vicious shouting, the strumming, the slamming, the pounding, the battling with insolent archfiends, the avalanche breaking down the door, the proddings from under the bed, and always, outside, the cries, the wailing, the terrible music, the dark’s spinets:

Satan.

So stretcht out huge in length the Arch-fiend lay Chain’d on the burning Lake,

In disobedience to his God, Did man himself call down the rod? Or did th’ arch-fiend, from Heav’n that fell, Inspire the mischief to rebel?

A diabolically evil person.

1690, anonymous translator, The Royal Wanton (attributed to Gregorio Leti), London: F.B., Part 5, p. 48, […] her Arch-fiend and Devil of a Lord, had impudently sent the same Villain to abuse her once again.

So this is a plot to shield this arch-fiend, and I have detected it. A word from me, and three heads besides his would roll from their shoulders!