Six Lessons from Madame LaGrange - S5-E22
Character mistake: The SS guard salutes Major Hochstetter with his palm out, in the British fashion. Firstly, German soldiers salute palm-down, secondly, by the Wehrmacht (and SS) military protocol, he should just click his heels and not salute at all when receiving an order.
Six Lessons from Madame LaGrange - S5-E22
Factual error: Hilda is writing with her left hand. At the time of the Third Reich, it was still the practice in Germany to force left-handed children to learn to write with their right hand.
Six Lessons from Madame LaGrange - S5-E22
Continuity mistake: When Hogan is talking with Lily Frankel before the double agent comes over, Hogan is lifting his beer. When the camera goes to close up, he's lifting it again. Also, in the long shot, the beer is down about three quarters of an inch from the rim. In the close up, the beer is nearly full.
Answer: Nimrod's actual identity was never revealed in the series. It was only known that he was a British intelligence agent. Nimrod was not Colonel Klink. Hogan had only implied it was him as a ruse to get Klink returned as camp commandant, not wanting him replaced by someone more competent who would impede the Heroes war activities. The term "nimrod" is also slang for a nerdy, doofus type of person, though it's unclear why that was his code name.
raywest ★
"Nimrod" is originally a king and hero mentioned in the Tanach and taken into the Bible and the Koran. His name is often used in the sense of "stalker," "hunter," and sometimes figuratively as "womanizer" as in "hunter of women." I've never seen it used to denote a nerdy person, and although I cannot disprove that connotation, I think given his role, the traditional meaning is more likely the intended one.
Doc ★
It's widespread enough that Wikipedia has an entire section on it: https://en.wikipedia.org/wiki/Nimrod#In_popular_culture