The 43rd, a Moving Story - S1-E23
Character mistake: When Klink explains the route of the trucks carrying the red cross packages to Kühn, he for once uses a map actually showing Germany. Unfortunately, the places he points to start near Luxemburg and track all across Germany. The spot he places Hammelburg at would be near Poznan in Poland.
The 43rd, a Moving Story - S1-E23
Revealing mistake: As Carter and Newkirk sit by the wall catching their breath, a seam can be seen running vertically where two wall sections meet behind them.
The 43rd, a Moving Story - S1-E23
Other mistake: When Hogan uses the water barrel periscope to spot Manor Kuhn, the first shot is from an impossible angle.
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