Short answers, pulled from the story.
L. L. Zamenhof, a Jewish ophthalmologist, created the Esperanto language during the late 1870s and early 1880s while living in Białystok. He published the first book of Esperanto grammar in Warsaw on the 2nd of May 1887 under the pseudonym Dr. Esperanto.
Nazi Germany banned Esperanto legally in 1935 because Adolf Hitler viewed it as an example of international Jewish conspiracy in Mein Kampf. Esperantists were killed during the Holocaust with Zamenhof's family specifically targeted for execution by the regime.
Sidney S. Culbert estimated between one and two million people speak Esperanto at Foreign Service Level three proficiency over twenty years of testing. Marcus Sikosek challenged this figure suggesting only about 1,600 fluent speakers exist worldwide if distributed evenly.
Duolingo launched its free Esperanto course for English speakers on the 28th of May 2015 reaching 350,000 registered learners by the 25th of March 2016. By July 2018 that number rose to 1.36 million students studying through the platform.
The green five-pointed star against white canton proposed by Richard Geoghegan in 1887 became the most commonly used flag approved by delegates at Boulogne-sur-Mer in 1905. This symbol represents the movement and remains the standard flag for Esperantists today.