A mantradraṣtā (mantradrasta; seer of mantra) ṛṣi (seer-sage). Āyu(Ayu) was one of the seer-sages belonging to the Caraka branch of Kṛṣṇa-Yajurveda (Krishna-Yajurveda).

Brahmāṇḍapurāṇa (Maharṣi)(1.33.13)