Green’s Dictionary of Slang

a general interrogatory intensifier; a var. on what the devil...? phr.

1681		Otway Soldier’s Fortune II i: Smooth rogue! who the devil is this fellow?
1688		T. Shadwell Squire of Alsatia I i: Who the devil would have thought this put durst have drawn a sword?
1709		S. Centlivre Busy Body III i: Who the Devil lives here?
1721		Penkethman’s Jests 18: Who the devil expected Set Forms in a Meeting-house.
1748		Smollett Roderick Random (1979) 54: Who the devil are you?
1762		Bridges Homer Travestie (1764) I 60: But who the d—l durst say no, Since angry Jove would have it so.
1858		A. Mayhew Paved with Gold 156: Who the devil’s that French fellow?
1879		C.J. Kickham Knocknagow 229: An’ who the divil cares what you or the likes of you agree with?
1986		F. Taylor Auf Wiedersehen Pet Two 309: ‘Who the devil’s Hazel?’ thundered Ally.