As recounted in an earlier installment of Comic Book Urban Legends Revealed, the Superman radio show held the first appearances of many characters and themes that would later appear in the Superman comic book.
One of those ideas was kryptonite, which appeared years before it made its way into the comic book. However, in this instance, the radio show was beaten to the idea by the comic, just not in a published comic book (which Jamie Coville pointed out to me when the original Urban Legend installment came out about the radio series).
You see, in the above unpublished story where Lois discovers Clark's identity, there is a meteor that comes to earth made up of metal called "K-Metal," and its radiation takes away Superman's powers, and Superman deduces it is from his home planet.
While the story was never published, the story stayed with DC (as Mark Waid came across it many years later still at DC), and there is a definite chance that the radio writers ran with the idea a few years later, when kryptonite was introduced in 1943, but they just as likely could have come up with the idea independently of Siegel's script.
Well, that's it for this week, thanks for stopping by!
Feel free to drop off any urban legends you'd like to see featured!