A hatter in 19th century England was a professional who made and fixed hats, and hatters used a glue which over time caused them to act crazy (mad). A person who acts as if they are crazy (mad) is "mad as a hatter." Example: "Wow- did you see that guy on the corner?" Answer: "Yeah, he was as mad as a hatter." Lewis Carroll, in his popular children's book Alice In Wonderland, used the image of "mad as a hatter" to create the character that he called The Mad Hatter. Example: "Everybody in my family knew that our uncle was as mad as a hatter."