1940

Batman’s side-kick boy wonder Robin first appeared in Detective Comics Issue No. 38. Bill Finger’s addition of Robin was an attempt to make Batman less of a creature of the night and more of a father figure. The 40s also brought a more defined character, more muscles, and longer bat ears.

1940

The best of the Rogues Gallery, the Joker first appears in Batman Issue No. 1 along with Batman’s future love interest, Catwoman, then just called The Cat.

1940

Actor Basil Karlo, also known as the first Clayface, appears in Detective Comics Issue No. 40.

1941

Short and squatty, the Penguin, aka Oswald Cobblebot, first appears in Detective Comics Issue No. 58.