Polish physician and oculist who created the most important of the international artificial languages— Esperanto.

A Jew whose family spoke Russian and lived in an environment of racial and national conflict on the Polish-Russian borderland, Zamenhof dedicated himself to promoting tolerance, mainly through the development of an international language. After years of experiment in devising such a tongue, working under the pseudonym of Doktoro Esperanto, he published an expository textbook, Lingvo Internacia (1887; Dr. Esperanto's International Language). His pseudonym, Esperanto (“【one】 who hopes”), was to become the language's name.

In addition to continuing his medical career, Zamenhof worked to develop Esperanto and organize its adherents. The first Esperanto magazine appeared in 1889, the beginnings of formal organization in 1893. With some literary and linguistic skill, Zamenhof developed and tested his new language by translating a large number of works, including the Old Testament, Hamlet, Hans Christian Andersen's Fairy Tales, and plays of Molière, Goethe, and Nikolay Gogol. At the first international Esperanto congress at Boulogne, France (1905), and at successive annual congresses in various European cities, Zamenhof delivered a number of memorable addresses, but he renounced formal leadership of the Esperanto movement at Kraków, Pol., in 1912. His Fundamento de Esperanto (1905; 17th ed., 1979; “Basis of Esperanto”) established the principles of Esperanto structure and formation.