Jack 'Gorilla' Grant is an agent with MI6.
He is, at least, when we first meet him. That will change a wee bit as time goes along but considering the department's attitude towards him from the get-go, it can always change back again. It is the early-to-mid 60's and the Cold War is still raging hot so agents like Grant are always in demand but it being the 60's, England being England, apes like Grant are not decidedly not in fashion and are an embarrassment and must be purged from the ranks - until someone of his qualifications are needed again.
The word 'ape' is apt for Grant for a couple of related reasons. First is his nickname and covername of 'Gorilla'. Some thought that the title came from the disdain that the career intelligence officials had for people they thought of as working at the "coalface". A labourer, a knuckle dragger, a rock crusher, an ape to do the heavy lifting. Someone to come in and do the manual, dirty work, the jobs that they deemed beneath themselves, but which was far more suited to some "oik" from the army." The truth was that "he wanted a cryptonym that was unique to him and unobtrusive in the general scheme of things. Of course in the great bureaucracy that was a secret government service he was given a rather bland code number - 2308 - which would forever be used on official communiques. However, things had taken a fateful turn when some wag in Personnel had discovered that Grant's nickname during his time in the army had been 'Gorilla' and had scrawled it onto the buff folder that held his life story."
The reason he had the nickname in the military was pretty obvious to anyone watching him for any amount of time. Grant is described as being a relatively small, stocky man (though in another place it refers to him as 'trim'), in his early-thirties and definitely in good shape. The name 'Gorilla' "fitted him like a glove, not because of his size or bulk, but more to do with his rolling gait when he walked, the furrowed glower behind the sunglasses, and the hint of a hirsute nature from beneath his well tailored suit".
Grant has white-blond hair which he keeps short and cropped leaving his scalp with a perpetual burned look. Not being impressive in his size and overall demeanor, Grant is able to pull off one of his best talents, that of being a spectre by which I mean he has an "almost intuitive skill to become noticeable". When he wanted to blend in, he did, simple as that. One of his instructors at the intelligence training facility commented that "you could lose him in a crowd of two people".
Grant's adventures are referred to as the Redaction Chronicles. In modern parlance redaction refers to the annoying black stripes obscuring important information on a document. In the case of Grant and his work with MI-6 during the 60's, redaction is not editing text for concealment but removing a person from the living.