It all begins here, with Fantastic Four #1. Sure, there were Marvel Comics before it. There were even many, many Captain America comics before it. But this comic, where Stan Lee, Jack Kirby, and inker Dick Ayers teamed up for the first time, marks the start of the real Marvel Universe.
The story was simple: Reed Richards of Central City, later changed to New York City without comment, gets his buddy Ben Grimm (who is a pilot), his lover Susan Storm (who has some kind of scientific background), and her brother (inexplicably) to jump in a rocketship. During their flight, they hit a belt of cosmic rays that mutates them into the world’s first superhero family.
Then, they get home and fight Mole-Man on Monster Island.
Yes, all that happens in a single issue. The first 100 issues of F4 are generally regarded as some of the best comic books of all time.
Also, there’s no mention of there having been other superheroes in the world before them. The concept of a “shared universe” is not yet born.
Also, this becomes important. Trust me. Eventually, when you click the tag “Thing In A Hole,” lots of stuff will come up…
Creators: Stan Lee, Jack Kirby
First appearances: Mr. Fantastic, Invisible Woman, Human Torch, Thing, Mole Man