Green’s Dictionary of Slang

(Aus.) the typical Australian male; used in WWI for an Aus. soldier, thus Bill, Jim and Harry, typical/average Aus. males.

1898		Bulletin (Sydney) 12 Mar. 14/3: Billjim saddled his favourite cuddy [...] and struck the Bushman’s rest at dawn next day.
[1899		H. Lawson ‘Jimmy Grimshaw’s Wooing’ in Roderick (1972) 450: His mates and the casual Jims and Bills were taken too suddenly to laugh].
1902		Bulletin (Sydney) 29 Nov. 11/1: The damsel gives her name as Eileen James, but as nobody knows any James who has lost a small girl, and as no one has claimed her, it seems to be another exposition of the tired feeling that characterises the great tribe of Bill-Jim, alias James.
1903		‘Dads Wayback’ in Sun. Times (Sydney) 11 Oct. 6/3: Ther eddicated poet is never read by Bill, Jim, an’ Harry.
1907		H. Lawson ‘The Stranger’s Friend’ in Lone Hand Nov. 17/2: A certain man from Anywhere, call him Biljim, [...] leaves a sick mate at the Half-Way Pub.
1914		H. Lawson ‘A Few Remarks on Bill and Jim’ in Roderick (1972) 717: In the first place, there isn’t, and never was, any ‘Biljim’. He’s a monster that was invented by some alleged writer who never knew either Bill or Jim, and is equally unknown to them.
[1916		C.J. Dennis ‘The Push’ in Moods of Ginger Mick 40: An’ there’s Bills an’ Jims an’ Bennos, an’ there’s Roys an’ ’Arolds too, / An’ they’re cobbers, an’ they’re brothers, an’ Australians thro’ an thro’].
1917		Feilding Star (N.Z.) 3 Mar. 2/5: A long, hungry, Billjim wandered into the new Australian Y.M.C.A. hut.
1918		Kia Ora Coo-ee 15 Apr. 4/3: [O]ne of the Billjims, who had a forty horse-power whisky thirst, was sent back to the L.H. dump at Rafa for a spell.
[1919		Aussie 12 Mar. 11/1: [caption] Two cobbers, Bill and Jim, in normal condition].
1920		Bulletin (Sydney) 19 Feb. 16/3: McDougall, returned Billjim [...] held a temporary job in Melbourne as a grievance-redresser for fellows-Diggers.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 22: Bill Jim: An Australian. (Australian slang).
1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.