Superman succeeded in establishing a vast, detailed world with a rich history that surrounds aliens and metahumans. It even introduced several iconic comic book characters with roots far beyond Superman’s, including the Green Lantern, Hawkgirl, Mr. Terrific, Metamorpho, and the Engineer. This was all done on planet Earth.

In a recent interview, James Gunn clarified that Supergirl is canonically younger than Superman in the DCU. He says that approaching the question from this angle is "assuming that everybody on Krypton is the same,