Other mistake: Hogan is listening to Klink's office with the coffee pot, and the clear top is still on the basket that is the speaker, but you can hear Klink.
Other mistake: When the General arrives at Camp 13 and is greeted by Klink, he notices Hogan and ask Klink who he is. Klink only says he's the Senior POW, the General sends his Aide to get Hogan. The Aide addresses Hogan by name, but Klink never said Hogan's name. (00:07:40)
A Klink, a Bomb and a Short Fuse - S2-E8
Other mistake: After Burkhalter gives Klink the order to help disarm the bomb, the camera cuts to Hogan and Klink. Between them and over the barracks, you can see the Desilu water tower.
Don't Forget to Write - S2-E13
Other mistake: When the recruiting officer is talking to Klink, Hogan and company listen in, as usual. The problem is the coffee pot. Any other time, they take off the top, take out the basket (which is the speaker) and plug in the power: this time, they forgot to remove the top to hear it, which would have muffled the sound. But the conversation was heard just the same.
Other mistake: When the boys are listening to Klink's office, the lid is on the speaker instead of being off.
Hogan and the Lady Doctor - S2-E20
Other mistake: As Hogan and company listen to Klink's office, the lid is on the speaker, so they shouldn't have been heard or at all.
Heil Klink - S2-E22
Other mistake: When the camera pans left following Brauner's car, you can see palm trees in the background. The area the Stalag is supposed to be in wouldn't have palm trees.
Everyone Has a Brother-in-Law - S2-E23
Other mistake: When the boys are listening on the coffee pot, the red light to indicate power is not lit.
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