Commander John Craig is an agent with Alert Command.
That, in turn , is part of the Investigation Corps, an elite outfit inside the military organization, United Worlds Space Fleets. Alert Command is the agency that sends in people to learn what the problem is and who is causing it. Then, if the situation is big enough or dire enough, units from the Fleet can come in to blow up the bad guys. If that is not feasible or prudent, it would fall on the agent on the ground to take care of matters him/herself.
Craig is "a big man, with pale blond hair cropped close to his head, his prominent jaw giving him the look of a fighter. Just so might a gladiator have appeared in pre-space days ... with his skin so brown and the muscles bulging even in his neck". He loves his missions but also loves to return to his home planet, Earth, and the loving arms of his long time girl friend, Elva Marlowe, a fashion designer whose creations were "the rage of fifty continents".
At least in the first adventure. Something changed before the second of the two recorded stories takes place.
In that subsequent mission, Craig is a bruiser of a guy who enjoys a good drink in a bar with a lovely lady, a good fight in a bar over the lovely lady, and then time alone with that lovely lady to make it all worthwhile. He gets his share of drinks, fights, and ladies in his missions. He and the love of his life Elva had broken up because unlike the man he was before who could not wait to get home to her, now he hardly ever took vacations, preferring to be out where the action was.
In the second adventure, by far the more action filled one of the two, he and his fellow agents have LOOT (League Of Outer-space Thieves) to fight. Their agents seem to be everywhere and was "the most important single branch of criminal activity in the Empire. It was an octopus with a thousand, perhaps even a million tentacles reaching through space to one planet and another, dipping into their cities and their lonely places." An awesome agent like Craig needs an awesome opponent.