The Old Gods or Nu'ada (those of Anui) are an ancient grouping of primordial spirits that share kinship to the gods of our Existence (Mundus), the ones known as Ae'ada. They are led by Chakravartin, God of Authority, law, and Order. They come from an existential plane beyond our own, and to be the direct first creations of Anui and Sargeras.
During the War of Deceit, the Old Gods waged war Aetherius on the grounds that the Divines were not taking care of their creations, and that the only way to save itself from destruction was to exert complete control over it.
The war in Heaven ended when Chakravartin was killed by Anurel, and the other Old Gods retreated back to wherever they came from. And now after the return of Sargeras and the Burning Crusade, it is believed that all or most of the Nu'ada have been destroyed.