Jock Saunders is an agent with British Intelligence.
More specifically, he is one of the very select operatives working during the Second World War directly under the command of spymaster Sir . That leader, codename Carnation, commands a group of agents who remain largely unnamed to those outside the organization and are known as the Men of Flowers (occasionally Men of the Flowers) as each member was given a flower name as his codename. For Saunders, that designation is Jasmine. He is given the codenumber of 23 - what that number implies, if anything, is not known.
Saunders is depicted a bit differently in the two adventures we have seen of him. In the first he is a rugged looking man with short buzz-cut blond hair and clean shaven. In the second, he seems more of a middle-aged man though still in impressive shape; he enjoys a full head of blond hair and is always sporting a bushy handlebar mustache with carefully cultivated upturns on the side. I am sure this changing of appearance tells us something important about the man and/or his method of operation going about his work but what that something is escapes me and is probably not important. What is important is that he is a dedicated field agent willing to put his life on the line for King and Country and does so on several occasions.
In one adventure he has the help of an assistant named Helen Marks, a young but capable blonde-haired woman. Why she is assigned to him on one instance and not the other is never mentioned.
Another matter never mentioned is anything dealing with Saunders' life before we meet him as a Flowers operative. He obviously had a life before the War and his entry into the organization; we are just never told anything about it.