Johnny Nero is an agent with MI-5.
Former agent is the way we should put it because when we first meet him, he has long since resigned from the department and now lives a life of luxury. Inheriting a fortune and then turning it into an even bigger one will allow a person to do that and Nero, not being an idiot, did so right away. Unfortunately for him but very lucky for his old boss, not to mention the fate of the Free World on occasion, Nero is first and foremost a man of action and while lying on the beach basking in the hot sun can be appealing, it is nothing as compared to putting his life in danger and testing his skills against dangerous adversaries.
Nero is approximately 35 years old though the depictions tend to shift a bit on that matter. We know that because, according to the info given in a "looking-back" tale told towards the end of the run, around eight years prior to our meeting him, he was 27. He was born in London in 1931, "educated Whitgift School, South Croydon, and Exeter University ... outstanding sports: Boxing, swimming, foils. Received short service commission Army Intelligence Corps, 1953. Overseas service: Aden and Suez. Seconded to M.I.5 1955."
How many years of those eight years he spent in MI-5 is not known but however many there were, they had to have been eventful considering the way that his former boss, Colonel Jason, thinks of him first when a mission comes up. Also pointing the age meter up a few notches is the fact that he has been in the business world long enough to have become bored with the lack of physical action as well as confident enough to know he can take the occasional side job without his "day job" suffering.
When not jet-setting around the globe for fun or on one of Jason's nearly suicidal missions, Nero likes to relax at his posh Kensington Garden abode - known in the parlance of the day as his "groovy pad". He has the services of his highly talented and quite appealing business secretary, Jenny Bird. This young but skilled woman, likely in her early to mid 20s, is impulsive and often reckless when it comes to her own safety because she is constantly forcing herself into the missions from which Nero tries very much to keep her safe. He is good at many things but stopping her is not one.
Interestingly, when it comes to Jenny Bird, though, Nero is extremely protective, wanting her to remain his secretary and out of harm's way. This despite the fact that on several occasions, she actually helps out a great deal, including saving his life more than once and even killing a man to save Nero.
As we first see Nero in action, he has the use of a fair number of handy little gadgets provided by MI-5 experts like a belt buckle that can be used as a lock-pick and a "needle-like spike" in the toe of his shoe, activated by the tap on his heel. His pipe is not used for smoking but for a communication device back to headquarters. His hairbrush has a recording/transmitting device in the base. As time and the missions move along, though, his use of such tools drops away leaving him with standard action-fiction methods like fists and knives and guns.
While the hair styles and the clothing show the activity as taking place in the mid 70s, the plots and the adversaries are as topical now as they were then. The Cold War may be over and thus the "other side" not quite the same but criminals and terrorists and power-hungry despots still ply their trade just the same as they did back when Nero fought them.