Don Q is an agent with the Diplomatic Service.
Now, what exactly the Diplomatic Service is remains a mystery. It is not, apparently, solely American but America is a major part. So is Britain. So, too, are the other Allies. Whoever is in charge of this department or bureau is never shown nor is much information about it given except to state that it is very much against the Axis, or as they are called, the Dictator Countries.
When we first meet Don Q (and that is all we ever hear him called - no last name and no explanation as to what the "Q" means) he is just finishing his training to replace his father, a well-known and highly respected American diplomat who was instrumental in negotiating oil shipments for base locations on behalf of his country. As he grew older, the man introduced his son to the same line of work so he could take over. The elder man was assassinated on an ocean-liner heading to Europe in the first adventure and Don Q accosted and dispatched the killers and then moved to find out who had hired them, starting his new line of work.
Suddenly (we actually do not know how long passes so it may have not been suddenly) Don Q is a well known man of mystery (oxymoron there). He is described as "a modern musketeer in search of high romance with a flare for any adventure." One report describes his adventures as "his unending missions of diplomacy" which invariably involve guns and fisticuffs and bombs and mayhem.
Don Q does not fight the good fight alone. In the second episode, he makes use of a French taxi driver named Pierre to foil the bad guys, including handing the control of a plane to him and telling a non-pilot to take over. In the third episode, without explanation, Pierre is now his "faithful" valet. Pierre, a Frenchman and resident of Marseilles, does call opponents "ya lugs!" and has other American aphorisms. But he fits well with Don Q for both like a good brawl.
Dashing looking and impeccably dressed at all times, Don Q does cut an impressive figure, including always have a monocle over his right eye. The fact that he looks an awful lot like and acts an awful lot like fellow international man of mystery, Black X, is undoubtedly a coincidence. But then there is the monocle over the right eye. And use of a single consonant for a last name.