The idiom “mad as a hatter” was around long before Carroll started writing. Colloquially used to describe an eccentric person, “mad as a hatter” is based on a problem that arose in the 1800s when hat companies used lead in the hat-making process. The lead got into their systems and they went insane, hence the term “mad as a hatter”.
The Mad Hatter asks Alice several times, “Why is a raven like a writing-desk?” Carroll admitted that there never was an answer to this classic riddle. However, after being badgered by fans for long, Carroll put an answer in the preface of the later editions. The answer was: “Because both produce a few notes, though they are very flat and it is ‘nevar’ put with the wrong end in front!”
The Mad Hatter comic book character made his debut in Batman #49 in 1948. He is the supervillain who keeps his Wonderland counterpart’s costume and personality, with a lot of his gadgets stored in his hat. In the world of Batman, he is a scientist who uses mind-controlling devices to manipulate his victims.