Continuity mistake: When Helga brings in Klink's dinner and sits it down, Klink takes off his monocle. In the close up, it's on and his hands are folded, then he points to a chess piece, contemplating a move. In the wide shot, he's holding his monocle, and puts it on.
Continuity mistake: Col Hogan eats Col Klink's chicken leg and places it back on the plate with meat still on the bone. When Col Klink picks up the chicken leg after, there is no meat on the bone. It's stripped bare. (00:01:00 - 00:03:00)
Continuity mistake: When Hogan drinks Klink's wine, he picks up the glass with his right hand and his left arm is behind him. A second later, Hogan's left hand is in front of his chest.
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