The Valar is the name given to the chief Ainur following their descent to Arda. The Ainur were holy spirits created by the supreme deity Eru Ilúvatar (see Ainulindalë). The most powerful of the Valar was Melkor; however he turned to evil, and therefore ceased to be considered one. Except for him, there were fourteen other Valar, whose existence was aimed at good.
Everything created by Ilúvatar had both male and female forms. Thus, there were 7 male Valar, and 7 female ones (Valier). Some of the Valar were considered siblings or spouses, yet it is not clear what such relations could mean. Of the 14, 8 had the greatest might (they were called Aratar). Each of the Aratar was responsible for some attribute of life in Arda, such as crafts and mining or agricultural growth. The king of the Valar was Manwë.
In addition to the Valar, there were Ainur of lesser might called the Maiar. The Valar ruled over the Maiar, who were their students and assistants in governing Arda. The Valar (and initially Melkor) had the ability to change their physical appearance, or to bear no shape at all. This was also true for some of the Maiar; however their abilities were not limitless. Some of the Maiar bore the form of animals (Huan, the hound of the Valar, and the Eagles of Manwë).