The Azerbaijanis speak Azerbaijani, a Turkic language descended from the Western Oghuz Turkic language that became established in Azerbaijan in the 11th and 12th century CE. Early Oghuz was mainly an oral language, and the later compiled epics and heroic stories of Dede Korkut probably derive from an oral tradition. The first accepted Oghuz Turkic text goes back to the 15th century. The first written, classical Azerbaijani literature arose after the Mongol invasion. Some of the earliest Azerbaijani writings trace back to the poet Nasimi (died 1417) and then decades later Fuzûlî (1483–1556). Ismail I, Shah of Safavid Iran wrote Azerbaijani poetry under the pen name "Khatâ'i".