Other mistake: The scene in Klink's quarters is one of a few where you can see Larry Hovis' (Carter) wedding ring.
Continuity mistake: After Hogan, LeBeau, and Newkirk leave, Carter is sitting, holding the glass with both hands. After the cut, he's holding the glass in his right hand only.
Visible crew/equipment: After Hogan goes down into the tunnel in Klink's quarters, the stove moves back in place. As it does, the wire on the floor pulling the stove back in place is visible.
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