Jan Baudouin de Courtenay

Jan Niecisław Ignacy Baudouin de Courtenay, also Ivan Alexandrovich Baudouin de Courtenay (Russian: Иван Александрович Бодуэн де Куртенэ; 13 March 1845 – 3 November 1929), was a Polish linguist and Slavist, best known for his theory of the phoneme and phonetic alternations.

For most of his life Baudouin de Courtenay worked at Imperial Russian universities: Kazan (1874–1883), Dorpat (now Estonia) (1883–1893), Kraków (1893–1899) in Austria-Hungary, and St. Petersburg (1900–1918). In 1919–1929 he was a professor at the re-established University of Warsaw in an again independent Poland.