Although the character of Batman was introduced in Detective Comics #27 in 1939, he wouldn’t get his own self-titled comic until the year after — where Batman and Robin’s first story pitched them against a new foe: the maniacal Joker. Bob Kane’s iconic, clown-esque design was inspired by Conrad Veidt’s Gwynplaine in the 1928 silent movie The Man Who Laughs and Bill Finger, who co-created the character and wrote the comics, planned for the Joker to die in the first issue. The Joker was stabbed through the heart, but an editorial decision lead to a hastily added panel showing the character survived the attack.
The Joker went on to become a recurring villain, and soon the archenemy of Batman and Robin. In his earliest days, he was also a ruthless killer — many of his crimes involved killing people. But when Jack Schiff became Batman’s editor, the Joker started softening, largely committing non-lethal crimes so that the comic could be marketed to children. The softening of the Joker would be fully completed in the mid 50’s with the introduction of the Comics Code Authority, banning gore and excessive violence in comic books. The Joker was no longer a killer but a thieving trickster, a much more camp and light-hearted villain to go up against the blunted, less brutal Batman.