Mounted cavalry archers were regarded as the most effective military unit of pre-modern times. Combining long-range archery with the speed and maneuverability of horse riding, mounted horse archers were able to use hit-and-run tactics against forces that lacked either of those skills.
The mounted archer unit originated from nomads around Central Asia, first among the Assyrians and the Indo-Iranian peoples (Indians and Iranians), and then among the Altaic peoples (Turks and Mongols). Mounted archers played an instrumental role in, for example, Cyrus the Great founding the Persian Empire, the Parthians and Huns defeating Roman forces, and later Genghis Khan establishing the Mongol Empire (the largest land empire in history). After witnessing the effectiveness of mounted archers, several other civilizations eventually also adopted the mounted archer unit, including China, the Byzantine Empire, the Islamic Caliphate, and Japan.
Even after the development of gunpowder in the late Middle Ages, mounted archers remained effective, as early firearms had slower reload times than the bow & arrow. For example, even as late as the 19th century, the Native American Comanche mounted archers were able to hold their own against firearm using American forces. The mounted archer unit finally became obsolete with the development of quick-reloading guns in the late 19th century.