Short answers, pulled from the story.
The Varangians were Viking warriors, traders, and settlers who came mostly from present-day Sweden. They settled in territories of present-day Belarus, Russia, and Ukraine from the 8th and 9th centuries, founding the state of Kievan Rus' and forming the Byzantine Varangian Guard.
The Varangians controlled two major trade routes: the Volga trade route connecting the Baltic Sea to the Caspian Sea and the Islamic world, and the Dnieper and Dniester route leading to the Black Sea and Constantinople. These were the primary links connecting medieval Europe with the Abbasid Caliphate and the Byzantine Empire, and most of the silver coinage in the medieval West arrived via these routes.
The Varangian Guard served as personal bodyguards of Byzantine emperors from the 10th to the 14th centuries. Initially composed of Varangians from Kievan Rus', the guard shifted to include predominantly Anglo-Saxons after the Norman Conquest of England in 1066. The guard operated until at least the mid-14th century, and people in Constantinople were still identifying as Varangians as late as 1400.
According to the 12th-century Primary Chronicle, Rurik was the leader of a group of Varangians known as the Rus' who settled in Novgorod in 862. His relative Oleg conquered Kiev in 882 and established the state of Kievan Rus', which was then ruled by Rurik's descendants.
Ahmad ibn Fadlan wrote a first-person account of the Rus during his 921-922 travels from Baghdad. He described them as tall, fair, and ruddy, tattooed from toes to neck in dark green designs, and never separated from their axes, swords, and knives. He also recorded the only known first-person account of the Rus ship-burning funeral ceremony.
Varangian runestones are carved stone memorials raised in Sweden to commemorate warriors who served in or died during service with the Varangian Guard. The largest group is the Greece Runestones, with the oldest dating to before 1015 AD. Ed runestone U 104, dated to the period 1080-1130, is now held at the Ashmolean Museum in Oxford.