Paul Harris is a businessman, not a spy.
He and his older brother were born and raised in the Far East and spent the majority of their lives there. It was their father's business that brought them to that part of the world, a business that stretched from Japan through China south to Malaysia and Singapore.
During WWII, the young man suffered with his family from Japanese aggression, spending almost two years in a concentration camp after seeing his father die at the hands of the Emperor's soldiers. Many long and difficult months followed filled with constant beatings and deprivations.
After the war, the two brothers headed south to Singapore where they picked up what was left of their family's import/export business and turned it again into a very profitable enterprise. Though their success was not astronomical, it was nothing to sneeze at and it allowed them to indulge at some non-work related activities.
While there remained a considerable distrust of the Japanese people, it was the Communist government of China and its spreading influence in Indochina that was the target of the brothers and a substantial sideline in the arms smuggling world.
Harris is not a spy. Throughout the series of 13 books he maintains his occupation as a businessman first with a nose for intrigue second. However, that nose gets him involved in situations of international portent in every chronicle and that more than qualifies him for inclusion.
The books about Paul Harris deliver two items to the reader. The first is the suspense and intrigue which is extremely strong and enjoyable. The second is the familiarity with the region that the author possessed having lived in the Far East for all of his yearly years and much of his adult life. The distrust and prejudice held by many in Southeast Asia for both the Japanese and the Chinese is captured brilliantly in numerous adventures. Even better is the love and anger the author has for Japan itself.
Note: in 1963, series author, Gavin Black, wrote a screenplay for the British anthology series Suspense entitled Killer Lie Waiting which aired in April, 1963, which had as one of the main characters a person named "Smiler" Harris. This may or may not be connected to the Paul Harris series.