The Ainur were angelic spirits created by Eru Ilúvatar at the Beginning. The Ainur who subsequently entered the physical world of Middle-earth were the Valar (powers), though that term came to refer primarily to the mightiest among them. Lesser spirits were called the Maiar. Most of the Valar and Maiar withdrew from Middle-earth to the Undying Lands of Valinor, though some of the Maiar, such as the Wizards or Istari, Melian, the Balrogs, and the Dark Lord Sauron, assumed mortal forms to help or hinder the peoples of Middle-earth.