I Look Better in Basic Black - S1-E28
Revealing mistake: When Hogan, Newkirk and Lebeau are dressed as the three women captured by the Gestapo, demand the truck be stopped, the wide shot shows that the truck is already stopped, and shaken to simulate it stopping.
I Look Better in Basic Black - S1-E28
Revealing mistake: A very long fuse is laid down then lit by the boys to distract the guards. While it is burning, watch the fuse in the dirt - it is actually being pulled from offscreen to the right of the shot.
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