Mark Hood is an agent of Intertrust.
He is one of a handful of field agents working for the highly secret agency that was created by the then four nuclear powers as a protection against any person or group outside the four powers who might seek to use nuclear technology against them. Their budget was as high as their profile was low. Getting the job done was the only goal. Of the men who put their lives on the line, Hood was the very best.
Hood had the most ingenious cover to give him the ability to travel the world without being noticed. He had none. And getting noticed was not only acceptable, it was expected. Hood was a wealthy American playboy, educated at Oxford, who took as his career after university the task of being an international sportsman.
Auto racing at Le Mans, karate competitions in Tokyo, sail fishing in the Bahamas, and, most famously of all, one of the greatest living cricket players in England, were many of the activities that Hood took part in when he wasn't on a mission, and the type of activity he used to cover his movement when he was.
At other times, Hood exercised strenuously and compulsively to keep him body in the peak of condition. This included regular sessions at karate where he already owned a black belt and where he had made his hands and feet swift weapons of destruction.
Hood stands just over 6', is in perfect shape with big, wide shoulders and excellent proportions elsewhere. His age is not specified but he had served in the Navy during the Korean War. With the series opening around 1965, that would place him between 35 and 40 years old.