Action Comics #1, from 1938, is where Superman was first introduced to the world. Jerry Siegal and Joe Shuster had unsuccessfully tried to sell their character as a newspaper strip during the 1930's. They finally got National Publications, later to become DC, to publish their character in the new format of comic books and begin the superhero boom.
In the early 1960's I once showed my father a small article from Newsweek about a copy of Action Comics #1 selling for $1000. He was shocked and wondered how a "funny book" could be worth that much money. I can only imagine his reaction now that a copy of that comic book has sold for over $3,000,000.
Scanned pencils, digital finishes.Sesame Street characters @ Sesame Workshop