Superman is about as iconic as you can get. He transcends the super hero medium of comics and offers a reflection of a nostalgic mid century America that never really existed. To many people he embodies the very values and presence of an America that we wished was real.
Which is all the more impressive when you consider that depite his outward resemblance to us, he is not human. Tossing about city buses and swimming in lava aside, it's sometimes easy to forget that Kal-El was born on Krypton and launched from that dying world to our own in a suped up* space crib. I think the residents of Smallville and Metropolis both can thank their lucky stars that the instinctual behavior of Kryptonian infants didn't include punching and staring intently at the ceiling until it catches on fire.
How much would it blow your mind though, if I told you that Superman was originally conceived of as a HUMAN?! Is your mind blown? Is it laying about the floor like the contents of a can of beans left unopened on a burner for too long?**
The totally awesome website Lettersofnote.com has featured, and translated, a letter that Jerry Siegel wrote to Russel Keaton in 1934. Siegel was looking for an artist for Superman and pitched the idea to the Buck Rogers artist with a brief script detailing a significantly different origin story for Clark Kent.
Notable differences include Kent being human, instead of alien, thrust back in time from a dying earth by the last man alive. Thankfully the last man alive was not a telephone repair man, and he had the capacity and resources to construct a time machines. Additionally, this Clark Kent was raised in an orphanage, and delighted in public displays of his strength.
Keaton turned down the offer, and it was another four years before Superman finally ended up with Joe Shuster and National Allied Publications.
* See what I did there? I'm very clever.
** My father actually did this. Big mess. Beans everywhere. Beans!
Superman: The Man of Tomorrow [Lettersofnote.com]