Rod Renton is an agent with the Missile Defense Systems.
The MDS is a British intelligence agency, almost certainly connected to the military. We learn very little about the organization except through conjecture. It is obviously large enough to be able to have resident agents in many major cities around the world and it is funded well enough to give its agents some pretty interesting and impressive toys with which to play. It is referred to as being "secret" though it is not known whether that means its existence is kept quiet or just that not much is known about it is not disclosed.
Renton is said to be the MDS's best agent, especially when partnered with the junior but still very capable Mac Malloy. Renton is definitely the man in charge but he trusts and relies on Malloy enough to show that Malloy could easily have led his own team though Malloy is refered to in both recorded adventures as his assistant.
Both Renton and Malloy are trained pilots, able to handle both winged and rotor machines. They are crack shots and not at all shabby at hand-to-hand combat. In keeping with the requirements of being an agent in the 60s, Renton has an arsenal of very nifty "secret" devices which he is able to produce when the going get tough. If nothing is at hand, his hands can work wonders at opening locks and closing mouths.
The fact that the two cases we know about deal with the Middle East and the Far East shows that Renton is an international traveller, sent anywhere in the world there is trouble but especially when the evil forces of the "East" are getting frisky and endangering the interests of the "West".