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.
1818		T Creevey diary 9 Sept. in Maxwell Creevey Papers (1903) I 282: The Dutchess of Kent had an old, ugly German female companion with her, and the Duke of Wellington was going about amongst his staff before dinner, saying—‘Who the devil is to take out the maid of honor [sic]?’.
1825		H. Wilson Memoirs I 188: Mr Ward [...] hoped he had kept nobody waiting? To be sure not, said Alvanly, who the devil would wait for you?
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.