Each day in June you'll get an entry showing you the first appearance of seemingly minor characters, phrases, objects or events that later became notable parts of comic book lore. Not major stuff like "the first appearance of Superman," but rather, "the first time someone said, 'Avengers Assemble!'" or "the first appearance of Batman's giant penny" or "the first appearance of Alfred Pennyworth" or "the first time Spider-Man's face was shown half-Spidey/half-Peter." Stuff like that. Here is an archive of what I've featured so far.
First reference to Batman living in Gotham City
Surprisingly, it was not until 1940's Detective Comics #48 that Batman was said to be living and working in Gotham City.
The above crooks have come to Gotham to blackmail a singer to use as leverage against a guy they took prisoner back in Kentucky. Luckily, the singer is friends with Bruce Wayne, so Batman gets involved. _________________________________________________________________________________
First appearance of the famous "In Brightest Day, in Blackest Night" Green Lantern Oath
As you may or may not know, the original "In Brightest Day, in Blackest Night" oath was not Hal Jordan's, but Alan Scott!
Alan Scott went through a couple of oaths before settling on this one in 1943's Green Lantern #9...
First reference to the Hulk getting stronger as he gets madder
From pretty early on, Stan Lee established that the Hulk was nearly unstoppable. In 1964's Tales to Astonish #59, he showed us just how...
After re-using the phrase in #70, it was not used again until Hulk was well into his solo series._________________________________________________________________________________
Feel free to send in ideas for future debuts I should feature here to firstname.lastname@example.org!