Like Jack, pet form of John, Joe, familiar abbreviation of Joseph, is colloquially used as a generic term for a lad, a fellow, a chap.
According to the text in which occurs the earliest use of Joe Soap that I have found, this name originated in the slang of the British armed forces during the Second World War, and was originally applied to an unintelligent person (cf. the term sad sack, which originated in U.S. Army slang). This text is the column The Lighter Side, published in the Nottingham Evening Post (Nottingham, Nottinghamshire, England) of Monday 16th August 1943:
If the fighting services in this war are not quite so strong on war songs as we were in the last, it may be largely due to the fact of mechanisation, and the consequent lack of the same route-marching incentive to rhythmic melody. But apparently they make up for this by developing far more extensive service slang.
After this war civilians may be confounded by the conversation of the ex-Service youth of both sexes, for the women auxiliaries are picking up most of their masculine comrades’ slang.
A “Joe Soap” indicates a “dumb” or unintelligent person. A “midwaaf,” on the other hand, is just an over-officious A.T.S. * non-com. A “Zizz” is a rest period or a slacker’s paradise. One excellent invention is “Attery,” which is the living quarters, of course, of the A.T.S. Sausages, which were “Bangers” to all old-school-tie disciples, become in the service slang “Barkers,” and machine-gun bullets are “confetti,” the latter a pretty descriptive touch.
* A.T.S.: the Auxiliary Territorial Service, i.e., the women’s branch of the British Army during the Second World War.
However, according to later texts, Joe Soap was applied to any ordinary soldier of the lowest ranks:
1-: From The Western Gazette (Yeovil, Somerset, England) of Friday 28th December 1945:
The Western Gazette has been paid the compliment of the gift of a copy of “The Story of the Seventh Battalion of the Somerset Light Infantry,” in so far as it relates to the achievements of the unit from the Normandy invasion to the conclusion of hostilities.
This handsome book is not for sale. It is for the 7th Somersets and their next of kin. It is, as its compiler, Captain J. L. J. Meredith, writes, “dedicated to ‘Joe Soap,’ the man whose name you will not find on any page, of whom there is no mention in the awards and decorations, whose work was never noticed but whose job was well done. To his wife and family and friends, and the people of France, Belgium, and Holland who cheered him on his way.”
2-: From A Jungle “Opera” That Was Never Sung, by ‘R. G. W’, published in the Yorkshire Evening Post (Leeds, Yorkshire, England) of Wednesday 13th March 1946—in the British Army, gunner designates all privates of artillery:
“Let’s write an opera,” said Michael to me one evening in the canteen. We were in the middle of a jungle in India, sipping tea and eating sandwiches. Opera seemed out of place.
But I said “O.K. […].”
The basic plot was simple. It dealt with the rise to the rank of major of Gunner Joe Soap and the decline to the rank of gunner of Major Roder-Hedd. The final scene was intended to show the War Office how the Army should be run!
3-: From New Army Act ‘Inevitable’, by a solicitor, published in the Reveille (London, England) of Thursday 3rd October 1946:
When the Air Council refuses to reopen Mr. Pensotti’s case the very pinnacle of callousness and pigheadedness is reached. Here you have a rising young barrister of really excellent character, who very properly joins up when war is declared. By 1941 he becomes a Judge-Advocate. Then he offends a senior officer, and certain very serious accusations are made. He is court-martialled and dismissed the service.
If the affair is not reported in the Press, owing to his being overseas, the award becomes public because it is gazetted. The unfortunate and undoubtedly innocent gentleman has a life of misery until he is cleared as far as his profession is concerned by the Parliament of Benchers (several of them being High Court Judges).
He then petitions the Ministry, but the petition is rejected. The latest we have heard is that this hopeless collection of troglodytes has again rejected the honest lawyer’s plea.
If this type of abuse can cripple temporarily an eminent barrister career, what chance has the average Joe Soap who offends an N.C.O. [= non-commissioned officer] or an officer, either at home or abroad?
4-: From the column Seen and Heard, published in the Belfast Telegraph (Belfast, County Antrim, Northern Ireland) of Thursday 5th December 1946:
No one will deny that life to-day is fairly closely bound by red tape. There were never so many laws, regulations and rules to comply with—never so many forms to be filled In. The suggestion has been made—and it is not a bad one—that every time the Government put a new form into circulation they should also publish a number of specimen copies, typical examples already filled in. This would go a long way towards simplifying matters for members of the general public.
The system that is adopted in the Army is not unlike this. When a particularly difficult form turns up for completion by the troops guidance examples are invariably posted on orderly room boards under the “signature” of a widely-known fictitious character:—“Private Joe Soap.”
The earliest occurrence that I have found of Joe Soap as a generic name for an average man is from the column From Day to Day, published in The Nottingham Journal (Nottingham, Nottinghamshire, England) of Saturday 12th April 1947:
What is […] surprising […] is [Councillor Dutton’s] assertion that a Corporation official is correct in expressing support in public for a committee recommendation before it has received the approval of the Council.
It is true, of course, that the Press is in a privileged position in being able to comment upon proposals which have still to come before the Council, but it is a privilege which is shared by members of the Council and by the public.
Thus, Coun. Dutton or any other member of the Council, or Mr. Joe Soap, as an ordinary ratepayer, or “Day to Day,” as a commentator, are all free to express opinions on a proposition to come before the Council—but it is a different matter to say that a Corporation official is equally entitled to do so.