What is "rugii"

The Rugii, also Rugians, Rygir, Ulmerugi, or Holmrygir (, ) were an East Germanic tribe who also appeared in southwest Norway and who in 100 AD lived near the Vistula River south of the Baltic Sea in an area, 900 years later, known as Pomerania. A number of them went from the Baltic Sea to the Danube River valley, where they established their own kingdom in the 5th century AD.