Green’s Dictionary of Slang

a general intensifier for a question; var. on what the hell...? phr.

1841		F.L.G. Swells Night Out n.p.: ‘Who the h-- are you?’ &c. and which, if returned [...] answered by ‘Ax my a---,’ or some such elegant retort.
1869		J. Greenwood Seven Curses of London 202: Who the h[ell] would take notice of a w[hore] kicking the bucket?
1874		‘A.P.’ [Arthur Pember] Mysteries and Miseries 338: ‘Holloa, cap!’ I called out, sitting up in the wagon. ‘Who the hell’s that?’ was the polite rejoinder.
1913		A. Lunn Harrovians 197: Who the hell are you? You’re only a priv on sufferance.
1929		W.R. Burnett Little Caesar (1932) 22: Who the hell’s Villa?
1932		V.F. Nelson Prison Days and Nights 29: Who the hell is So-and-So that he should have all that power?
1947		I. Shulman Amboy Dukes 9: Who the hell is asking you?
1949		R. Chandler Little Sister 26: Who the hell are you?
1959		J. Osborne World of Paul Slickey Act II: You may not have the prowess but who’s the hell to guess.
1960		H.S. Thompson letter 25 May in Proud Highway (1997) 216: Who the hell is he engaged to?
1970		G.F. Newman Sir, You Bastard 60: Who the bloody hell are you?
1999		Guardian Sport 8 Jan. 16: Who the bleedin’ ’ell are you?
2000		Guardian Rev. 7 Jan. 14: So, who the hell are they?