Who is Āsuri Brāhmaṇa and why did Lord Kapila exposit sāṅkhya to the same?

Question

Śrīmad-Bhāgavatam says here (quoted below)

pañcamaḥ kapilo nāma
siddheśaḥ kāla-viplutam
provācāsuraye sāṅkhyaṁ
tattva-grāma-vinirṇayam

that is,

Lord Kapila, foremost among perfected beings, gave an exposition of the creative elements and metaphysics to Āsuri Brāhmaṇa.

Īśvara Kṛṣṇa's Sāṁkhya Kārikā verse 70 reads as follows:

Etat pavitram agryam, munir āsuraye anukampayā pradadau |
āsurir api pañcaśikhāya tena bahulīkṛtaṃ tantram |70|

that is,

This foremost, purifying doctrine, the sage (Kapila) imparted to Āsuri out of compassion; Āsuri taught it to Pañcaśikhā, by whom this doctrine was propounded extensively.

Who is Āsuri Brāhmaṇa and why did Lord Kapila exposit sāṅkhya to the same?

Answer 1

This is partial answer.

Who is Āsuri Brāhmaṇa?

Asuri was maharshi in Samkhya doctrine. For one thousand years Asuri Brahmana performed Sacrifice called panchasrota. He also had vision of ultimate Truth and expounded the same to sages.

Chapter 218 (Ganguli Edition) or Chapter 211 (Bibek Debroy Edition), Santi Parva of Mahabharata provides some info about Asuri. Quoting Bibek Debroy's translation:

There was a great sage named Panchashikha, the son of Kapila. Having travelled the entire earth, he came to Mithila. He had ascertained the true knowledge about all kinds of dharma connected with renunciation. He had settled all the meanings, was free from opposite sentiments (Like pleasure and pain, happiness and unhappiness), and all his doubts had been dispelled. He was said to be the only rishi who was beyond the desire that characterizes humans. He desired the ultimate and eternal happiness that was so difficult to obtain. People were astounded at his form and thought that he was the supreme rishi, Prajapati Kapila, who expounded samkhya, himself.

He was the first disciple of Asuri and was said to be immortal. For one thousand years, he (Asuri) had performed the sacrifice known as panchasrota (Literally, the one with five flows, a description of the mind.). There was a circle of the followers of Kapila and they were seated. They wished to hear from him about the supreme being, who was not manifest. Because of his own sacrifices and austerities, the sage had become successful. He had obtained divine sight and had understood the difference between kshetra and kshetrajna. The single Akshara of the brahman is seen in many different forms. In that circle, Asuri spoke about the one who is not manifest.

There was a brahmana lady by the name of kapilā and she was Asuri’s wife. Panchashikha became his disciple and suckled milk at her breast. Because he suckled milk from the breasts of Kapila’s wife, he came to be known as his son and obtained supreme intelligence. The illustrious one told me about how he became Kapila’s son. He also told me about how Kapila’s son obtained every kind of supreme prosperity.

Here kapila is used as synonymous to Asuri since kapilā was his wife. Kapila (means who is tawny) is not Lord Kapila here.

Answer 2

Gaudapada's Samkhy Karika Bhashya says Asuri was a Brahmana born in Kapila's family:

Virtue, knowledge, renunciation and power were born with Kapila. Thus born, seeing this world sinking in the blinding gloom and the succession of samsāra (birth and death), he became filled with compassion and taught this knowledge of twenty-five principles to the brahmin Āsuri, born in his own family,—the knowledge by which misery comes to an end.

As far as how Asuri became a shishya of Kabila, here is what the Suvarna Saptati, an ancient commentary on the Samkhya Karika of unknown authorship, says:

There was formerly a wise ascetic called Kapila, born of heaven, innately endowed with the qualities: law, knowledge, impassivity, existence by himself, these four qualities constituting his self. Seeing humanity plunged in blind darkness he experienced for it a great compassion. "Alas! They live and die in blind inking thus, he looked round the world, and discovered Asuri, brahmin by birth, who had sacrificed to heaven regularly for a thousand years. Disguising himself, he approached the brahmin, and addressed to him these words: "O Asuri, thought amusest thyself with leading the life of a master of a house." Having spoken, he withdrew without receiving any reply. After another thousand years, he returned and repeated the same words. On hearing them, the brahmin replied: "O, honoured of the world, indeed I enjoy the life of the master of a house." The ascetic heard him and went back in silence. Some time after, he returned, repeating the same words, and received the same reply. Kapila asked: "Canst thou maintain thyself pure, and live the life of a Brahmacharin?" "I can," replied Asuri. Thenceforward he renounced the way of his family and commenced the ascetic observance, as a disciple of Kapila.

Talk about stubborn!