Gunston 'Gun' Cotton is an agent with the British Secret Service.
He is most of the time, in most of the recorded adventures that exist about this interesting man. He could also easily be labeled as an adventurer for while Cotton spends a good deal of his time working on behalf of the British Government in clandestine matters, he also is not adverse to going off on his own, well, usually in company with friends, looking for excitement and things to challenge himself.
On the first page in the very first tale we learn an interesting bit of information about him. "There was something unusually engaging about the man who now, leaning well back, stretched his legs across the [train] carriage. Lazy brown eyes, a mouth that seemed ready to smile - altogether an attractive rather than a handsome face. Even in the drab uniformity of modern dress, his delightfully careless manner - not to people but to life - gave him an air of almost insolent unconcern all the more interesting for the knowledge tht he could be surprisingly unconventional."
Cotton, we are told, came from money, as the expression goes. His family was quite well off and he enjoyed a very comfortable upbringing. That came to an end suddenly but luckily briefly when upon his father's unexpected passing Cotton learned that his father had left him just "a sheaf of debts". After a week of "disillusion and dismay" he learned that his father's brother had also passed away and left Cotton with a sizeable inheritance; "there was money now to keep his mother in luxury and still some over for him to squander". At that point, "the next few years he spend wandering from one country to another in pursuit of knowledge and experience, unknowingly preparing himself for what was to follow".
When he is actually working for the intelligence community, Cotton answers directly to a man high up in an unnamed department within that community, so secret in fact the identity of that man is not revealed; he is identified simply as 'X'. This 'X', "who learned his job from a certain 'C', was the one who first decided Cotton had what it took to be an independant operative. It was 'X' who approached him with the idea and, upon acceptance, got busy "preparing him for months in different branches of information, ['X'] knew that the seed he had sown in Cotton has been planted in rich soil."
This recruitment came after Cotton's involvement in the Great War came to a sudden and definite end. Being a renowned and capable airplane pilot, Cotton had been a valued asset in the nascent British Royal Air Force until "a deadly duel in which he had been worsted" put him on the ground for a time likely recovering, followed by the end of the War. The excitement and thrills Cotton had felt during that action had been intoxicating and the paucity of it afterwards had irked him. Even getting his own plane, a Moth, and winning a few Daily Mail contests had not sufficed. Hence his eagerness in accepting the offer from 'X'.
Cotton's first set of work was simply to continue his travels about Europe and just "have a look round. Why not do a little sketching?" After a time, the things Cotton would be asked to do would increase until he would become the highly valued and useful operative we find him to be at the beginning of those recorded missions.