The Evolution of the Joker

It's had many iterations through the years. Comics Alliance looks at them a little more deeply.

From the piece...

The Joker remained pretty consistent throughout the Golden Age, vexing Batman and the police with the unpredictability and spectacle of his crimes, and becoming sillier, more colorful, and larger-than-life along the way. Batman and the Joker maintained a Holmes-Moriarty dynamic, and on more than a couple of occasions, the Joker appeared to have died, with no body found. In Detective Comics 168, in 1951, it was revealed that he had once been a criminal called the Red Hood, and revealed an origin of sorts: 10 years earlier, costumed as the Red Hood, the attempted robbery of a playing card company led to Batman's intervention and a leap into chemical waste runoff, and the Red Hood emerged with bleached skin, green hair, and a new outlook on life. In truth, it wasn't a great story, and really seems almost unnecessary. But some interesting broad strokes were put in place, and the chemical bonds that linked Batman and the Joker were given new strength.

With the administrative heat on comics in the late forties/early fifties, Joker's homicidal tendencies were seriously curtailed. With the enactment of the Comics Code Authority, violence and mayhem were lanced from the form, and throughout the Silver Age the diabolical monster was reduced to a mildly threatening trickster. Some good stories were still told using this tamer version, and great groundwork was laid for broadening the culture's awareness. While no longer a serial murderer, he was still crazy. The addition of schtick like trick guns, acid-spitting posies, and silly, elaborate crimes added to the mythos and over-the-top personality of Batman's defining archvillain. This was the Joker that made the transition to television in Cesar Romero's 1966 portrayal, adding a cackling soundtrack to the clumsy ha-ha-has that had been mocking Batman and the Boy Blunder (hah!...classic) since 1940. By the early 1970s, though, the character's use had tapered off significantly.