I expect the derivation of "Tommy Atkins" has probably been mentioned before on the cat, but it seems to fit in here.

At one time when soldiers signed up, they were presented with a form to fill in. Form filling and of course literacy were fairly rare at that time, so one part of the form was an example and filled out in the name of an imaginary Thomas Atkins. It is said that many recruits (especially if they were illiterate) merely copied the letters from the example and therefore signed on in that name.