Colt is an officer with the U.S. Military Intelligence.
Normally I would have mentioned the individual's first name but that piece of data is missing about him. It is certainly not the only information we lack concerning this intrepid guardian of security. In fact, his last name is one of the few things we do know.
First, from his depiction we know that he is a sturdy, solidly built man with a strong rugged face. Sturdy chin and piercing eyes and a demeanor that warns against messing with him. I would put his age around 30 years old.
Second, he appears to be a career man for the activities we can follow him in take place before the start of open hostilities and it took a while to get advancement in the peacetime military. Speaking of rank, when we first meet him, he holds the rank of Captain. He did so well in that mission that his commanding general tells him at its conclusion that he deserves a promotion. The next adventure has him with the rank of Major.
Third, his area of expertise in the military seems rather wide. In the first story he is deeply involved in the development of and security for a new artillery weapon. In the second one, he is the man to call when three dozen planes are stolen and he quickly dons a flight suit and leaps into the cockpit of another plane to chase them, engaging in a dogfight along the way.
Fourth and final note, if he had not been in the military, it is likely he would have gone into the private eye business due to the tenacity he shows in hunting the bad guys and the patter he spews when involved in fistfights with them, not to mention the fact that he gets hit over the head and knocked out a lot as was common in that profession.