The original Joker is not just a completely insane clown. He was built as an educated person with an extremely intelligent mind. Joker is sensitive to scientific knowledge, especially chemistry, obsessed with art and even obsessed with … jewelry. In the first comics and the 1966 TV version of ABC, he turned into a naive, disruptive villain with ridiculous tricks to play pranks on people instead of being a crazy killer like present.

Source: Punchtee.com