Jan Niecisław Baudouin de Courtenay

Jan Niecisław Ignacy Baudouin de Courtenay 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 Tartu, 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 a once again independent Poland.