Āyu is one of the sons born of Urvaśī , sired by Purūravā. In Brahmaṇḍapurāṇa, Vāyupurāṇa, Viṣṇupurāṇa and Bhāgavatapurāṇa it is said that Āyu is the eldest of the six sons of Urvaśī and Purūravā. However, Matsyapurāṇa says that Āyu is the eldest of the eight sons of Urvaśī and Purūravā. In Vāyupurāṇa and Brahmāṇḍapurāṇa it is said that Āyu and his younger brothers, being sons of Urvaśī, were known as Gandharva (a kind of demi-gods).

In Mahābhārata it has been said that five sons of Āyu, namely, Nahuṣa, Gaya, Vṛddhaśarmā, Raji and Anenā were born out of the womb of Svarbhānavī (Prabhā, according to Brahmāṇḍapurāṇa), daughter of Svarbhānu or Rāhu. In Brahmāṇḍapurāṇa, Bhāgavatapurāṇa and Viṣṇupurāṇa , too, the names of Nahuṣa, Kṣatravṛddha, Rambha, Rajī, and Anenā have been mentioned as five sons of Āyu. In another reading of Vāyupurāṇa, it has been said that Amāvasu is the son of Āyu. However, in Matsyapurāṇa, Vṛddhaśarmā in place of Kṣatravṛddha, Vipāpma in place of Anenā, and Dambha in place of Rambha have been used.  In Padmapurāṇa, the name of Indumatī has been mentioned as the wife of Āyu.

For the benefit of humankind, God Brahmā gave to God Viṣṇu the first sword created by Śiva. Viṣṇu again gave that sword to Marīci. In this course, it came to Pururavā. From Pururavā, Āyu got this sword, and from Āyu, Nahuṣa received this. In Śāntiparva it has been said that Āyu was one of those who got established in society by virtue of tapasyā.

In Anuśāśannaparva of Mahābhārata, Āyu was one of those kings who rejected eating meat in the month of Kārtika or in Śuklapakṣa.

Nahuṣa, the eldest son of king Āyu, got the kingship of the heavenly kingdom, in the absence of Indra.

Āyu is one of those famous kings whose names are to be remembered every morning, as mentioned in Anuśāsanaparva.