Chester 'Chet' Gordon is an agent with the FBI.
As an agent with the Bureau, his duty could take him anywhere in the country going up against all sorts of criminals and crimes but we learn early on that his specialty seems to be counter-espionage, or the catching of spies operating inside the U.S. borders.
Exactly how long he has been doing this type of investigation is not stated but we are told that "8 or 9 years" before we first meet him he had been in college so it is safe to guess that he has been with the FBI for around 4-6 years. This would put his entry into federal work somewhere between 1937 and 1939 since the activities we first learn of his happen in 1943.
Gordon is a very self-assured man, entering each conversation with neither nervousness nor cockiness. There is one time, though when he is said to have quietly entered a room "with a contemptuously calm look in his black eyes".
Gordon is described as having an athletic physique, having been once an intercollegiate swimmer and having the "short-distance swimmer's broad shoulders and thin flanks" to show for it. He is further said to have a soft base voice which was often "diffident, and the long dark face from which it issued had an inward-looking, almost sullen look. Gordon had sleepy black eyes set deep in a burnished outdoor face. Black horse-tail hair receded from his narrow temples. His face was like an Indian's who distrusted all palefaces".
Said by Gordon while he pointed a gun at a man, "This gun is attuned to your aura, Mr. Drake. If you approach it it will go off".