The story of Y. R. Chao being, at one time, the only person in the world who could speak the current standard version of Mandarin:
Chao: … I mentioned the addition of the entering tone (in addition to the first, second, third and fourth tones) with glottal stop endings. Those were the main features of this artificial [guóyīn 國音], and I made a special set of records for it and a textbook to go with it.
Levenson: Was that the first set in 1923?
Chao: Yes, they were made in--I went to America in '21 and I made the record in New York with Columbia Phonograph Company.
Levenson: I've heard it said that you were the only person who could speak that language in the whole world. [Laughter] What were, to your mind, the primary objections to the artificial language?
Chao: For one thing, it was hard to find teachers who could speak it naturally. For example, when I made the records, I was the only person who could talk in that pronunciation, whereas, after the change, you had about one million speakers who would be possible teachers.
In Chinese linguist, phonologist, composer and author, Yuen Ren Chao, with an Introduction by Mary Haas; an Interview Conducted by Rosemary Levenson, (The Bancroft Library University of California, Berkeley; China Scholars Series), 1974: 76–77. On line at http://content.cdlib.org/view?docId=hb8779p27v&brand=calisphere&doc.view=entire_text (accessed 20131102).