David Gresham and James Wilkins are agents with British Intelligence.
They will be, shortly after the start of the first recorded adventure. They will not ask to be seconded from the British Army to the very nascent Military Intelligence which will later morph into MI6. Being officers in good standing and very much patriotic, they would never shirk from their transfer but there would be some consternation; they were soldiers and not spies, at least in the beginning.
The two meet while fighting in the Great War, specifically in waning days of 1915. An assault on Constantinople was in the works, the hope being to force the Ottoman Empire to leave the pact with Germany and Austria-hungary. While the sergeants of the Company they were both attached to were largely experienced fighters, most of the enlisted were very green and so were many of the officers. This includes Wilkins but not Gresham.
Wilkins was a Captain in the Company but was only 19 years old, "the youngest British officer serving i the Mediterranean". It was strongly believed by all that "achieved his rank through connections rather than merit since he was the youngest son of Lord Bartlett and a recent graduate of Eton (albeit the top student and a King's Scholar there)."
Gresham, a wee bit older at 22, held the rank of Lieutenant and was "the one man in the company who had previously fought in the front lines: He had been with the Lancashire Fusiliers in the trenches in France and had fought at Ypres; he'd been at Gravenstafel Ridge when the Germans had first used poison gas on the lines, and he'd even seen action at the Suez Canal".
Wilkins was "fair-haired, perfectly clean cut, well-educated, and the cream of British nobility". Gresham was "the bastard son of a very wealthy Manchester industrialist" whose "straggly coal black hair was too long, his chin was never freshly shaved, his mustache was grossly untrimmed and filthy".
Another point of difference is that Wilkins is usually soft-spoken and polite but amiable to all while Gresham was by nature "surly and quiet". The two make for an interesting pair.