Zamenhof was born in 1859 in the town of Bialystok, Poland (at the time Imperial Russia). Growing up, Zamenhof was saddened by the ethnic prejudices of the various groups living in Bialystock. Although his family belonged to the Yiddish-speaking Jewish majority, there were also large numbers of Poles, Germans, and Russians. Zamenhof believed that the primary reason for hatred between these populations was attributable to their inability to understand each other's languages.
(Zamenhof about 1879)
As early as his time at secondary school, he began work on crafting an international language and by 1878 he had nearly finished what he called the Lingwe Uniwersala. At that time, he was still too young to be recognized for his linguistic work, so he went on to study and practice ophthalmology in Polish Russia and Austria, all the while working on his international language.
In 1879, Zamenhof authored the first grammar of the Yiddish language and was active in Jewish affairs. A series of pogroms in Russia motivated Zamenhof to join with Zionists in 1882, but he left the Zionists five years later declaring that all forms of nationalism produced human unhappiness.
(Zamenhof's Unua Libro)
In 1887, his first international language textbook was published in Russian under the pseudonym "Doktoro Esperanto," which meant "Doctor Hopeful" in his created language. This book is now known by Esperantists (those who speak Esperanto) as the Unua Libro or the "first book." Over the next few years editions were published in English, Hebrew, German, Polish, French. Due to the catchy pseudonym Zamenhof used, the language became known as Esperanto. Zamenhof's goal was to create an easily learned and politically neutral second language for the purpose of uniting the people of the world.
Unfortunately for Esperantists, at the same time Esperanto was being advanced, English was increasingly becoming the new lingua franca and has largely fulfilled Zamenhof's goal of creating an international second language, albeit without the easily learned and politically neutral purposes envisioned by Zamenhof. Esperanto is supposedly five times easier to learn than other existing languages.
(First World Conference of Esperanto, 1905)
A World Congress of Esperanto was created in France in 1905 and has been held every year since excepting during the World Wars. Zamenhof in a bid to encourage its use, released his control over Esperanto and allowed the Esperanto community to dictate its development. Symbols of Esperanto were even created including a flag (a green star on a white canton imposed on a green field) and Esperantists often use the green star by itself or with with a letter "E" superimposed on the star.
Dr. Zamenhof died in 1917 in Warsaw and is buried there. Unfortunately, for obvious reasons, 20th century dictators took a particular dislike for Esperanto. Hitler wrote in Mein Kampf that the spread of Esperanto was a Jewish plot to destroy national differences, so they could assume control and when the German Army took control of Warsaw, the Gestapo received specific orders to find and eliminate the Zamenhof family. Zamenhof's son Adam was found and executed and his two daughters, Sofia and Lidia, were taken to Treblinka where they perished in the Holocaust.
Esperanto still emerges from time-to-time by advocates of internationalism or those who seek to downplay the prominence of English or traditional religion. It also appears in some movies and other media when a fictitious language would better serve to give the feeling of a non-specific foreign land. It was even used for an entire song in one of my more favorite movies, the 1940 comedy, Road to Singapore. Ironically, it was also used in the Charlie Chaplin film The Great Dictator, where the shop signs of the Jewish ghetto are in Esperanto