Ludwik Lejzer Zamenhof (,  – ), usually credited as L. L. Zamenhof, was a Polish physician, inventor, and writer. He is most widely known for creating Esperanto, the most successful constructed language in the world. He grew up fascinated by the idea of a world without war and believed that this could happen with the help of a new international auxiliary language, which he first developed in 1873 while still in school.