Re: It's a Bird, It's a Plane, It's the Superman Costume Thread! - Part 3
As far as I know, originally Superman finds out in the first kryptonite story in 1948, when he follows the path of the kryptonite meteor back to its source, traveling through time and arriving on Krypton as a phantom. Then in the silver age it was retconned that due to Superman's flawless memory, he could remember his short life on Krypton in perfect detail, which is probably a lot of the reason he identified first as a Kryptonian and second as Clark Kent.
Superman with realistic physics isn't Superman.