Mario Andrew Pei (1901–1978) was an Italian-American linguist and polyglot who wrote a number of popular books known for their accessibility to readers without a professional background in linguistics.
Pei was born in Rome, Italy, and emigrated to the United States with his parents in 1908. By the time that he was out of high school, he spoke not only English and his native Italian but also French and had studied Latin as well. Over the years, he became fluent in several other languages (including Spanish, Portuguese, Russian, and German) capable of speaking some 30 others, having become acquainted with the structure of at least 100 of the world's languages.
In 1923, he began his career teaching languages at City College of New York, and in 1928, he published his translation of Vittorio Ermete de Fiori's Mussolini: The Man of Destiny. Pei received his doctorate from Columbia University in 1937, focusing on Sanskrit, Old Church Slavonic, and Old French.
That year, he joined the Department of Romance Languages at Columbia University, becoming a full professor in 1952. In 1941, he published his first language book, The Italian Language. His facility with languages was in demand in World War II, and Pei served as a language consultant with two agencies of the Department of War. In this role, he wrote language textbooks, developed language courses, and wrote language guidebooks.
While working as a professor of Romance Philology at Columbia University, Pei wrote over 50 books, including the best-sellers The Story of Language (1949) and The Story of English (1952). His other books included Languages for War and Peace (1943), A Dictionary of Linguistics (written with Frank Gaynor, 1954), All About Language (1954), Invitation to Linguistics: A Basic Introduction to the Science of Language (1965), and Weasel Words: Saying What You Don't Mean (1978).
Pei penned The America We Lost: The Concerns of a Conservative (1968), a book advocating individualism and constitutional literalism. In the book, Pei denounces the income tax as well as communism and other forms of collectivism.
Pei and Esperanto
Pei was fond of Esperanto language. He wrote his positive views on it in his book called One Language for the World. He also wrote a 21-page pamphlet entirely on world language and Esperanto called Wanted: a World Language.
Value of neologisms
Of all the words that exist in any language only a bare minority are pure, unadulterated, original roots. The majority are "coined" words, forms that have been in one way or another created, augmented, cut down, combined, and recombined to convey new needed meanings, The language mint is more than a mint; it is a great manufacturing center, where all sorts of productive activities go on unceasingly.— 
Creative innovation and slang
While slang may be condemned by purists and schoolteachers, it should be remembered that it is a monument to the language's force of growth by creative innovation, a living example of the democratic, normally anonymous process of language change, and the chief means whereby all the languages spoken today have evolved from earlier tongues.— 
- The American road to peace: a constitution for the world, 1945, S.F. Vanni
- Swords of Anjou, 1953, John Day Company. Pei's first and only novel, praised in HISPANICA  as "an admirable combination of absorbing narrative and sound scholarship..."
- THE CONSUMER'S MANIFESTO: A Bill Of Rights to Protect the Consumer in the Wars Between Capital and Labor, 1960, Crown Publishers
- Our National Heritage, 22021, Houghton Mifflin
- America We Lost: The Concerns of a Conservative, 1968, World Publishing
- Tales of the natural and supernatural,, 1971, Devin-Adair
- Remarks on the Esperanto Symposium
- Mario Pei On Esperanto Education
- One Language For The World
- Pei Discography at Smithsonian Folkways