Introduction
Vayu is a Yazata of wind, the space between heaven and earth, and fate or time, notable among Zoroastrian divine beings for an unusual moral ambivalence: unlike most other Yazatas, who are firmly aligned with Ahura Mazda's goodness, Vayu is associated with both the life-giving breath that sustains living beings and the death that inevitably claims them.
Note: this Vayu shares his name and function with the Vedic and Hindu wind god Vayu, reflecting shared Indo-Iranian origins, though the two traditions developed the figure differently.
A dual nature
The Avesta describes Vayu as having, unusually, two aspects: a "good" Vayu associated with life-breath, beneficial wind and assistance to the righteous, and a more fearsome aspect associated with death and destruction, an ambivalence rare among the otherwise more clearly aligned Yazatas of the Zoroastrian system.
Association with fate and time
Vayu is also connected with the passage of time and the working of fate, an area of Zoroastrian thought that intersects with the broader and more fully developed later concept of Zurvan (Infinite Time), which some scholars see as related to or developing out of aspects of Vayu's domain.
Warrior god
Vayu is invoked in the Avesta as a swift and powerful warrior figure, called upon for aid in battle, reflecting the practical, this-worldly concerns of the wind and space he governs alongside his more abstract associations with fate.