L. L. Zamenhof was the creator of Esperanto, the most widely used constructed international auxiliary language.

Esperanto is the world's most widely spoken constructed international auxiliary language. Created by L. L. Zamenhof in 1887, it is intended to be a universal second language for international communication, or "the international language". Zamenhof first described the language in Dr. Esperanto's International Language, which he published under the pseudonym Doktoro Esperanto. Early adopters of the language liked the name Esperanto and soon used it to describe his language. The word esperanto translates into English as "one who hopes".