Jake Jeffords is an agent with the British Secret Service.
More specifically, he is one of the operatives working for a division of that organization called the X-Section, each member of the team being designated as an "X-agent" as the letter is at the beginning of each operative's codename. What exactly is the codename for Jeffords, though, is never revealed.
The X-Section has its secret headquarters in a concrete warren beneath the exclusive members-only Ashley's Club.
Jeffords answers to Sir Ralph Cowper-Dacier, known to his subordinates though never to his face as 'the Fat Man'. It is an appellation that is well deserved considering his heavy jowls and pronounced double chin. To say that the Fat Man is a unsympathetic task-master is to give him some slack.
Jeffords appears to be in his late 30s or early 40s. He has average length (for the mid-70s) black hair. He is quite fit physically and still very proficient with marital arts, especially karate at which he remains the Service's champion.
Reading the two recorded adventures shows a couple of interesting facts about Jeffords. The first is that he is intrepid almost to a fault. No promising clue will be ignored even if it means breaking into guarded enemy camps. The second is that Jeffords is highly prone to getting captured by the bad guys because he has that happen to him a great deal. And the third is that Jeffords is a very lucky man when it comes to finding ways to escape after being caught or in having someone show up to free him.
However he manages to survive, he is more than capable of finding a way to get the job done.