In Tolkien's fictional universe The Ainur were the first and mightiest beings created by Eru
Ilúvatar (the Creator & Father of All) in the depths of time before the beginning of the World.
The Ainur were the offspring of Ilúvatar's thought, and each was given understanding only
of that part of the mind of Ilúvatar from which he/she came.
The exception to this was Melkor, the greatest of the Ainur (later known as Morgoth, the first
Dark Lord) who had a part of the gifts of all the others. The World was created through the
"Music of the Ainur", music sung by the Ainur in response to themes introduced by Eru.
Those of the Ainur who felt concern for the Creation entered it, and became the Valar and the
Maiar, the Guardians of Creation.
Much of the world, though, was marred when Melkor sought power for himself alone and
battled with the Valar for ages until his brother Manwë, the Lord of Valar, with the help of
the other Valar & the Elves were able to banish Morgoth from the World signifying the end
of the First Era.