A "Hatter" is a person who makes or sells hats. Historically, the term is often associated with the hat-making industry in the 18th and 19th centuries, particularly in England. The profession became well-known due to the use of mercury in the hat-making process, which caused health issues for many hatters, leading to the phrase "mad as a hatter." The most famous fictional Hatter is the Mad Hatter from Lewis Carroll's "Alice's Adventures in Wonderland." This character is known for his eccentric behavior and whimsical tea parties. The Mad Hatter has become a symbol of creativity and madness in popular culture.