The Collector General - S3-E27
Trivia: In this episode, there is a German coat-of-arms on the wall with the bug in it. This is the only time it's seen.
Everybody Loves a Snowman - S3-E14
Trivia: For budgetary reasons, it was not unusual to see one actor play several different characters in a television series. Case in point, in this episode, Noam Pitlik plays the part of an escaped POW. In the pilot episode, he was a Gestapo agent, and various German officers in others.
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