Today is Superman's birthday. Well, not in the fictional world of DC Comics. In the narrative, the character's birthday is February 29th, but that's an article for another day. On this day, in 1939, the entertainment world changed forever when DC Comics—known at that time as National Allied Publications—released Action Comics #1.
The issue, beyond the first appearance of Superman, is considered a landmark for a variety of reasons. Prior to Action Comics #1, comic books didn't publish new material. The books served as collections of old strips from the newspaper. After Action Comics #1, the trend of comics compiling reprints practically vanished overnight.
The Superman of Action Comics #1 is highly divergent and paradoxically unchanged from the character that exists in modernity. Instead of battling bizarre villains, the Man of Tomorrow fights a domestic abuser and rescues a falsely imprisoned man from execution. The Superman of the 30s is a champion of the downtrodden and oppressed that uses his abilities to enrich lives. The character still possesses vestiges of that presentation, but the message of Superman's power has been overshadowed by the mandates of the genre he inspired. Fans are more focused on Superman battling science fiction creatures that can provide him physical opposition as opposed to stories that speak to the altruistic and selfless nature of the character.
In any event, without Action Comics hitting stands today in 1939, there'd be no MCU; there'd be no modern manga, and we'd be deprived of some of our most prized American colloquialisms that relate to the Man of Steel. If you can, find a copy of Action Comics #1 and give it a once over. Hell, even if you don't like Superman, there's a pretty sweet Zatara comic in there too.