Gerald Blair is an agent with the British Secret Service.
Though he appears still fairly young, his actions indicate that he is no newcomer to the cloak and dagger business. Blair is extremely comfortable operating in the European theater, moving from one country to another without any hesitation and showing he has familiarity with any region he visits, showing he has been doing this for some time despite his apparent young-ish age.
Blair moves quickly and easily. While not particularly tall, he is thin and sinewy and he shows on several occasions that he is fast in his reflexes and quite willing to take action without hesitation. He is in good shape despite routinely lighting up a cigarette.
Blair is obviously an intelligent man though in one scene after having to chase after a fleeing car and then finding the driver had set up a rifle ambush for him, all before fleeing in a third waiting car, Blair muses, "Somethin' funny ... could be I've stumbled on it." You think?
While as was the custom in the mid-60's, Blair routinely dresses in suit and tie, he tends to go with something more than traditional apparel. It it isn't a checked suit, it is a splashy tie. Nothing over-the-top by any means because he does have to tail people now and then and being crazily dressed would be a huge mistake. Nevertheless, he does seem to want to establish his own independence with his dress.
Blair has average length slightly wavy dark hair, though in a couple of instances it seems might not be all that dark so perhaps light to medium brown.