Comics

Newspaper Daily, Feb 01-02 1939Spanning from approximately 1938 - 1955 is the Golden Age of comics, the original Superman stories as started by Siegel and Shuster including the comic books and the daily newspaper comics.  (Some break this age period in half by the Golden Age, and the "Flux" age where they start setting up the Silver Age in the late forties.) 

This, of course, sees the first introduction of Clark Kent (Kal-L) and Lois Lane, and of course other milestones including Perry White and Jimmy Olsen.  The first comics start out in Cleveland where they work for the Daily Star, and later in the Daily Planet.  It is this age that set up Clark Kent as a disguise and Superman as the real man of the story; Lois of course falls for Superman who initially wants nothing to do with her.

Superman's Girlfriend: Lois Lane #086, coverSpanning from approximately 1955 - 1970 is the Silver Age, the time where Superman comics branched off into over half a dozen regular series.  It was during this period that the bredth of the Superman mythos was created and both Lois Lane and Jimmy Olsen were treated to their own serials.  Additionally this is the age that introduced Supergirl, the Superpets, and most of the backstories about Krypton.  Stories about many character's past exploits were told as this age developed the character's backstories, often in retcon.

This is also the beginnings of alternate universe stories - what was then called "Imaginary Stories" for the characters and exploring them fully.  Additionally, this age brought in many more cross-overs between characters as well as various temporary supernatural elements - temporary powers, aliens, monsters, look-a-likes, various forms of kryptonite as well as flashbacks.