Montagu Christie Butler, (b. 25 January 1884 in London, d. 5 May 1970) was a British academic, librarian, lexicographer, musician, and Esperantist. A winner of several prizes at the Royal Academy of Music in London, he was a harpist and a versatile music teacher skilled in playing various musical instruments, as well as a teacher of voice and of musical composition. He was a Quaker and a vegetarian who first became an Esperantist in 1905. From that time Butler taught Esperanto to students, eventually achieving near-native fluency and becoming the first truly bilingual Esperantist.