Nimrod is a biblical figure mentioned in the Book of Genesis and Books of Chronicles. The son of Cush and therefore a great-grandson of Noah, Nimrod was described as a king in the land of Shinar. The Bible states that he was "a mighty hunter before the Lord [and]... began to be mighty in the earth".

Some funny trivia with "might hunter": Bugs Bunny called Elmer Fudd nimrod, saying something like "nice shot, nimrod!" -- the insult was that Elmer was a bad hunter. But the obscure reference was lost on most people, much less a child audience (myself included), and so nimrod became a generic insult akin to "idiot" or "imbecile.