During the Dawn War, the Primordials created soldiers to act as their armies and allies. These beings of elemental might clothed in armor were called Archons, and their appearance devastated the mortals of Tol that were fighting on the side of the Gods. In retaliation, the Gods created the Angels to act as their vanguard in the battle against the Primordials and their might.
Faceless, genderless, and winged, the angels were powerful servants of the Gods indeed! They virtually embodied the powers of the Gods made manifest in unearthly flesh. They brought comfort to the mortals who had suffered the wrath of the Primordials and their archons, and they fought fiercely against archon, Giant, and Primordial alike.
After the war was ended, the angels remained, fierce and fearsome servants of the Gods. Each God, including the evil Gods, took a portion of the angelic host to be their servants and agents. With the threat of the Primordials largely ended, the angels now devote much of their time to doing the work of the Gods, including fighting the hordes of Demons that sometimes erupt from the Abyss and foiling the plots of the Devils. It is worth noting that, even though Asmodeus is technically a God, he is served by no angels. The angels of the Mourned God who might’ve been his were transformed into Devils.
The origin of the race known as Devas also lies in the more compassionate and loyal of angels.