Action Comics/YMMV

Ensemble Darkhorse -- Despite being on the cover, Superman was just one of a number of characters introduced in this book. Nobody really expected much success with him; in fact, Supes had already been rejected by a number of publications, and appeared here only because they really, really needed material. In fact, after the first issue, they kept him off the cover for a number of issues because of the uncertainty of his success.
Memetic Mutation: A weird case of it happening inside the industry. The cover of the first issue has been homage and parodied several times by other DC magazines, Marvel, and even in some cases the magazine itself decades later. It was even recreated in one of the early 21st Century Superman films. Of course, with Superman being the progenitor of the super-hero genre itself(at least if named that way, hello Gilgamesh), this is partially to be expected.