Apaosha

The primary account appears in the Tishtar (Tishtrya) Yasht (Yt. 8.21–29) in which Apaosha, named with the Avestan noun apaoša- ('not thriving'), confronts the star-divinity Tishtrya as Tishtrya rushes toward the cosmic sea Vourukhasha. They fight for three days and nights until Apaosha overcomes Tishtrya. Tishtrya complains to Ahura Mazda that human failure to give proper prayers and sacrifices weakened him; Ahura Mazda's sacrificial action enables Tishtrya to reengage and defeat Apaosha, after which rains fall. Later Middle Persian works (e.g., Bundahishn, Dadistan i denig as summarized in the provided material) integrate Apaosha into the broader creation-era war over waters, describe his allies and opponents, and in some later strands associate him astrologically (a specific Bundahishn tradition links him with the planet Mercury).

In the Avesta (Tishtar Yasht) Apaosha is personified as a 'horrible black horse with black ears and black tail' who opposes Tishtrya's 'mighty white horse with golden ears and golden tail.' The Avesta explicitly treats him as a Daeva. Later Middle Persian tradition maintains his personified, malign character but the supplied sources do not add a consistent alternate physical description beyond continuity of the adversarial figure.

Apaosha's primary role is as the active agent of drought—he can repel or overpower Tishtrya, prevent rains, and thereby cause failure of growth and prosperity. The Yasht recounts him defeating Tishtrya for several days; after being subsequently routed (following Ahura Mazda's sacrifice and Tishtrya's strengthened return), later tradition (Dadistan i denig 93) records an attempt by Apaosha to pervert rains into harm. Bundahishn narratives place him among the forces arrayed against the guardians of creation and name allies (e.g., Spenjagr) who act on his side; these allies can themselves be defeated by beneficent powers (e.g., by lightning). The mythic efficacy of Apaosha is explicitly influenced by human ritual behavior: omission of proper prayers and sacrifices weakens Tishtrya and thereby favors Apaosha's success.