Alan Douglas is British Agent 99, an agent with the British Secret Service.
Though a British citizen, Douglas is living and well entrenched in Hollywood in the U.S. being quite famous for the swashbuckling movies that made great use of his agility and athleticism. While making these highly successful adventure movies, Douglas also became well taught in the art of make-up and costuming, skills that would prove very useful in his later cloak and dagger endeavors where taking one another persona would get him into secret places or out of tight spots.
Douglas chose the entertainment business rather than the military like his much decorated and honored father, General Douglas of the British Royal Army, but it would be his father's service that would change the son's life. During the early battles between Britain and Germany at the start of WWII, the elder Douglas fell in battle and died. When, thousands of miles away, the younger Douglas heard of his parent's sacrifice, he decided he must put his movie career on hold and return home to do his part in the struggle.
Instead of joining the military, he applied to the British Secret Service (probably MI-6 but never mentioned) and was readily accepted. With his considerable acting skills, his abilities at disguise and his knowledge of numerous foreign languages, he was a natural to become a secret agent. The renown he had amassed for his movies would work both for and against him, though, as when not in disguise, he was instantly recognized wherever he went in Europe.
Willingly or coincidentally, Agent 99 becomes the nemesis of lead Gestapo agent Karl Vern from the first recorded adventure until the last, plaguing his enterprises and foiling them on several occasions.
In the last known operation, Alan Douglas is asked by President Roosevelt to assist in destroying a Gestapo spy ring operating in the U.S., starting with those up to no good in Hollywood, Douglas' old stomping grounds. There he again confronts Vern but he is assisted by a young costumed crime and spy fighter, the Black Cat, aka Hollywood movie star and America's sweetheart Linda Turner.