Jeff Curtiss is an agent with British Intelligence.
Most of the over three dozen recorded operations that exist for this man take place during the Second World War though his area of operation will change quite a few times showing that he definitely got around a lot. The European Theatre was where he would spend most of his time though he does make trips to the Indian subcontinent and even closer to the Japanese theater.
Curtiss is a Commander in the British Royal Navy where he is considered by many to be that service's "ace trouble-shooter", especially by one of his commanding officers in Military Intelligence, Colonel Quentin.
In addition to being an experienced naval officer, trained in and capable of taking command of a warship, he is also a very accomplished pilot able to sit in the cockpit of either a fighter or a bomber and get the job done. It is not unusual to see him switch gears (or vehicles) like that often in the course of an adventure. That does not mean, however, that he is the least bit out of his elements when he works on land dealing with groups like the French Resistance - Curtiss is good at his work no matter what environment he is put in.
Curtiss is an extremely fit man of normal height likely in his late 30s with wavy blond hair. He speaks both German and French well enough to be able, when needed, to impersonate either nationality. He also has working knowledge of several other languages making him able to function in other regions such as in Burma.
In just about all of his missions, Curtiss is partnered with Leading Seaman Ernie Black (roughly the equivalent of a corporal in the Army). Black is, from the looks of him, several years older than Curtiss but looks up Curtiss younger not just because of his far higher rank but also because Curtiss has shown him, obviously, how very good he is at his job.
Note: in the graphic adventures we have of Curtiss, the action takes place during WWII but in the few text adventures, they transpire at least a decade and a half if not more later. Curtiss and Black are still teammates and partners in these later missions.