Before the Creation, Eru Ilúvatar made the Ainur or "holy ones". This Quenya name comes from the Elvish root ayan- "revere, treat with awe". "Ainur only appears in plural [in Elvish texts] since after the Creation all those were Maiar includes Valar and their lesser kin, but not those who did not take part in the Great Theme, or else did not enter Eä." This means that only apocryphal texts written by Men and Hobbits used the singular Ainu.
The Universe was created through the Music of the Ainur or Ainulindalë, music sung by the Ainur in response to themes introduced by Eru. This universe, the song endowed with existence by Eru, was called Eä in Quenya. The Earth was called Arda. Those of the Ainur who felt concern for the Creation entered it, and became the Valar and the Maiar, the guardians of Creation.
The vala Melkor or Melko claimed the Earth for himself. His brother Manwë and several other Valar decided to confront him. Much of the world was marred by the conflict between the Valar and Melkor. According to The Silmarillion, the Valar and Maiar — with the aid of the Vala Tulkas, who entered the Creation last — were able to exile Morgoth, Melkor's physical manifestation, into the Void.