The Varangians or Varyags (; Greek: Βάραγγοι Varangoi, Βαριάγοι Variagoi) was the name given by Greeks and East Slavs to Vikings, who between the 9th and 11th centuries ruled the medieval state of Kievan Rus' and formed the Byzantine Varangian Guard. According to the 12th century Kievan Primary Chronicle, a group of Varangians known as the Rus' settled in Novgorod in 862 under the leadership of Rurik. Before Rurik, the Rus' might have ruled an earlier hypothetical polity. Rurik's relative Oleg conquered Kiev in 882 and established the state of Kievan Rus', which was later ruled by Rurik's descendants.
Engaging in trade, piracy, and mercenary activities, Varangians roamed the river systems and portages of Gardariki, as the areas north of the Black Sea were known in the Norse sagas. They controlled the Volga trade route (Route from the Varangians to the Arabs), connecting the Baltic to the Caspian Sea, and the Dnieper trade route (Route from the Varangians to the Greeks) leading to the Black Sea and Constantinople. Those were the critically important trade links at that time, connecting Medieval Europe with wealthy and developed Arab Caliphates and the Byzantine Empire; Most of the silver coinage in the West came from the East via those routes. Attracted by the riches of Constantinople, the Varangian Rus' initiated a number of Rus'-Byzantine Wars, some of which resulted in advantageous trade treaties. At least from the early 10th century many Varangians served as mercenaries in the Byzantine Army, constituting the elite Varangian Guard (the personal bodyguards of Byzantine Emperors). Eventually most of them, both in Byzantium and in Eastern Europe, were converted from paganism to Orthodox Christianity, culminating in the Christianization of Kievan Rus' in 988. Coinciding with the general decline of the Viking Age, the influx of Scandinavians to Rus' stopped, and Varangians were gradually assimilated by East Slavs by the late 11th century.