Roman Osipovich Jakobson (1896-1982) was a famous Russian linguist who emigrated to the Czech Republic and the United States. He was a leading figure of the Moscow Linguistic Circle, one of the two movements constituting Russian Formalism; he also was a founder of the "Prague school" of linguistic theory, whose other major figure was Nikolai Trubetzkoi.
Jakobson was one of the most influential intellectuals of the 20th century, with his contributions to linguistics, structuralist anthropology (he was an inspiration to Claude Levi-Strauss), literary theory and semiotics, among others.
Jakobson's three major ideas in linguistics play a major role in the field to this day: linguistic typology, markedness and linguistic universals. The three concepts are tightly intertwined: typology is the classification of languages in terms of shared grammatical features (as opposed to shared origin), markedness is (very roughly) a study of how certain forms of grammatical organization are more "natural" than others, and linguistic universals is the study of the general features of languages in the world.