Hatters are individuals who make or sell hats. Historically, the term is often associated with the hat-making industry, which was prominent in the 18th and 19th centuries. Hatters used various materials, such as felt, straw, and fabric, to create different styles of hats for various purposes, including fashion, protection from the elements, and social status. The phrase "mad as a hatter" originated from the effects of mercury used in the hat-making process, which could cause neurological damage. This phrase became popular in literature, notably in Lewis Carroll's "Alice's Adventures in Wonderland," where the character the Mad Hatter is a whimsical figure.