The Late Inspector General - S1-E4
Plot hole: At the beginning, the Inspector General instantly pegs the incidents Hogan's men enact as staged to defame Klink, and takes it as proof Klink is the right man to be put in charge of all POW camps in the Reich. Later, as Klink and he do their "final inspection", much less severe - and frankly, much less believable - incidents cause him to completely revise his assessment of Klink. Him believing Klink would be a pickpocket and compulsive kleptomaniac simply doesn't make sense.
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