The oldest of three sons, all called Vasubandhu, born in Purusapura (Peshwar) who were members of the Kausika family of Indian brahmins.  All three became Buddhist Bhikshus. Asanga's youngest brother was known as Virincivatsa, while the middle brother was known merely as Vasubandhu (see below).

  Asanga was a man who was endowed with the innate character of a Bodhisattva.  He became a Bhikshu of the Sarvastivada School, but afterwards he practiced meditation and became free from desire.  Though he investigated the doctrine of emptiness, he could not understand it.  He was about to commit suicide. Pindola, an Arhat, who was then in Eastern Purvavideha, having perceived this, came to him from that region and expounded the doctrine of emptiness peculiar to the Hinayana.  He arranged his thoughts according to what he was taught and at once comprehended it.  Though he had attained the doctrine of emptiness peculiar to the Hinayana, he, nevertheless, did not find comfort in it.  Thinking that it would not be right to drop the matter altogether, he went up to the Tusita Heaven using the supernatural power peculiar to the Hinayana and inquired of Maitreya, the Bodhisattva, who expounded for him the doctrine of emptiness belonging to the Mahayana.  When he returned to Jambudvipa, he investi-gated according to the methods explained to him and soon became enlightened.  While he was engaged in investigation, the earth began to quake (of its own accord) in six ways.  Since he understood the doctrine of emptiness, he called himself "Asanga", which means "without attachment". He afterwards often went up to the Tusita Heaven in order to ask Maitreya about the doctrines of the Mahayana sutras.  The Bodhisattva explained them extensively for him.  Whenever he acquired any new understanding, he would come back to Jambudvipa and teach it to others. Most of those hearing him did not believe him.  Asanga, Teacher of the Dharma, then prayed, saying, "I now intend to bring all beings to believe fully in the doctrine of the Mahayana.  I only pray that you, O Great Master, come down to Jambudvipa to expound the Mahayana so that all beings may become fully convinced of its truth." Maitreya, thereupon, in accordance with his prayer, came down to Jambudvipa at night, flooding it with great rays of light, had a large assembly of those connected with the Dharma called in a lecture hall, and began to recite the Saptadasabhumi-sutra.  After having recited a passage, he would explain its purport.  The seventeen bhumis were finished during the nights of four months.  Although all were together in one and the same hall listening to the discourse, it was, neverthe-less, only Asanga, Teacher of the Dharma,, who had access to the Bodhisattva Maitreya, while the others could merely hear him from afar.  At night, all together heard the religious discourse by Maitreya, while in the daytime Asanga, Teacher of the Dharma, commented once again, for the sake of others, upon what had been taught by the Bodhisattva.  In this way all the people could hear and believe in the doctrine of the Mahayana.  Maitreya, the Bodhisattva, taught Asanga, Teacher of the Dharma, to learn the "sunlight" samadhi.  As he learned according to what he had been taught, he subsequently attained entry into that samadhi.  After he attained entry into that samadhi, what he formerly could not understand all became intelligible.  Whatever he heard or saw was never forgotten, his memory having become retentive, whereas he formerly could not fully understand the sutras of the Mahayana, such as the Avatamsaka, previously taught by the Buddha. Maitreya explained for him all these in the Tusita heaven; thus the Teacher of the Dharma became well-versed in them and remembered them all.  Afterwards in Jambudvipa he composed several upadesa on the sutras of the Mahayana, in which he expounded all the teachings of the Mahayana taught by the Buddha. (Paramartha, "The Life of Vasubandhu", J. Takakusu, tr. [with some editing], pp. 273-275)