Scott Duncan is an agent with British Intelligence.
And that, I regret, is at present the most I can say about him. I have not found the three recorded adventures we know him to be involved in so I have no idea what the man is like or even what he looks like. He could be a she for all I know, though the name would indicate otherwise.
Okay, I do know that his adventures take place during the Second World War and since we see what we assume to be an image of him about to be shot by a German wearing a Nazi armband (which I think makes him more likely a Gestapo agent than a soldier), he is operating behind enemy lines.
And if that picture truly is of him, then we have pinpointed the sex to being male and a blond-haired fellow at that, in what seems to be good physical shape assuming he survives the likelihood of lead poisoning.