K27 is an agent with the British Secret Service.
What his real name is remains a mystery here and likely was so to anyone reading these adventures when they were first recorded throughout the length of the Second World War.
Not only do we not know his proper name, we are not certain of how to print his codename. We see it as "K27" in several spots, what looks like "K 27" once or twice, and as "K.27" on a few occasions.
In fact, we know very little about this man; where he comes from or how long has he been with the Intelligence outfit. As was not unusual for adventures of espionage agents recounted in the comicbooks of that era, we have no clue whether he was married or engaged or whether he was dedicated to doing his job, putting aside any personal attachments until the War was over.
He is shown to be a man with a strong, pronounced chin and a slightly hooked nose. In the couple occasions where we see him without his fedora, he has slicked back hair (one time it was jet black and one time it looked almost blond but that might have been a trick of the light).
K27's job with the Secret Service is that, obviously, of operative but in the limited evidence we have been able to uncover, one adventure has him in the role of a spy-hunter, seeking out a Nazi agent who has infiltrated England and was preparing a secret spy ring inside the country. On another occasion, though, he is deep inside Germany on a harrowing mission and striving to find a way out of that country. This tells us that his job is wherever he is needed regardless of it being defensive or offensive.
On at least two occasions we find K27 working closely with another operative. In one we are specifically told it is his assistant, Lieutenant Barlou, and it is likely still Barlou in the other.