In Mahābhārata and most of the Purāṇa(s), Amvarīṣa is the son of Nābhāga belonging to the Ikṣvāku clan.
amvarīṣañca nābhāgam (nābhāgim)
In Matsyapurāṇa, this Nābhāga has been called the son of Vaivasvata Manu, and elsewhere in the same chapter, he has been referred to as the son of Bhagīratha. In that line, Amvāriṣa would be the grandson of Bhagīratha. In another opinion, Amvarīṣa was the son of king Māndhātā, belonging to the Ikṣvāku clan. Purukutsa, Amvarīṣa and Mucukunda– these three sons were born of the womb of Vindumati (daughter of Śaśavindu). In Rāmāyaṇa, prior to the marriage of Rāma and Sītā– Vaśiṣṭha, while discussing the glory of the kings belonging to the Ikṣvāku clan, referred to Amvarīṣa as the son of Praśuśuka. But if we consult the genealogy provided in Purāṇa and Mahābhārata, the information given in Rāmāyaṇa should be reconsidered for authenticity, as it appears.

In Mahābhārata, at least three times– once in Ādiparva, secondly in Vanaparva and the next time, in Śāntiparva, Amvarīṣa has been mentioned as one of those renowed kings who had acquired great fame before their mortal end. Amvarīṣa was one of them.

He was a mighty king. Once he set out to war in a single chariot and defeated a million of kings at one stretched. These kings were all experienced in war. They surrounded him from all the sides. But Amvarīṣa was physically so powerful and such and expert in his weapon-skills, that he gave such a trouble to the opponent kings, and they had to come under his submission ultimately, stripped off their armours. Amvarīṣa was a religious minded king. After he got control over the world, he performed hundreds of yajña(s). Once he performed a yajña on the bank of river Yamunā.

In these yajñas performed by Amvarīṣa, brāhmaṇa(s) and others had food and drink at their will. The kings he defeated, he used to give them in charge of the yājñika brāhmaṇ(s). We think that since the kingdoms of the defeated kings were given away to the brāhmaṇa(s), those kings could be reestablished intheir kingdoms, and the brāhmaṇa(s) could function as the ̍control element̍ in the kṣatriya administration. It was perhaps keeping in mind this factor, it became proverbial that the way Amvarīṣa performed his yajñ(s), could not be done by anybody before him, nor would it be possible for anyone to do the same in future.

In Bhāgavatapurāṇ, king Amvarīṣa is a great devotee of God Viṣṇu, or Kṛṣṇa– the full incarnation of Viṣṇu. His name is mentioned in the context of the ninefold path of bhakti– smaraṇa, manana, and worshipping all the elements of bhakti with all the limbs of one̍s body.

He devoted his mind in the meditation of the lotus-feet of Kṛṣṇa, his words in uttering the praise of God Śrī  Hari, two hands in the cleaning of the temple of God, two ears in listening to the divine discourse, two eyes in beholding the temples of God, his limbs in the act of embracing the divine body of God, his noses in smelling the basil leaves offered at the feet of God, his tongue in the taste of God̍s prasāda, and his legs in walking around the places sacred to God,, and his head in the act of bowing to God. Along with yajña, dāna and tapasyā, this whole-hearted effort of devotion on the part of Amvarīṣa made him a selfless devotee. So, living as a householder, he was actually a renouncer of the world, and he could visualise God Śrī Hari in his own heart. Pleased with his devotion, God Śrī Hari gave him his Sudarśana cakra, to protect him from his enemies.

tasmā adāddhariścakraṃ pratyanīka-bhayavaham.

Once this king Amvarīṣa, after completing his Ekādaśī vrata and offering food and water to the brāhmaṇa(s) was about to break his fast, at that moment there came sage Durvāsā. Amvarīṣa humbly asked him to have his meal. Durvāsā went away to take a bath in the river Yamunā. There was only half a moment before the Dvādaśī tithi, but there was no sign of Durvāsā̍s coming back.

Amvarīṣa was in a dilemma. It was offensive to dishonour a brāhmaṇ-sage like Durvāsā, and not taking any food at the time of breaking the ritual fast– is also a violation of the vrata. So after consultation with the priests, he took some water, because taking water, according to the scholars, is considered as both ̍eating̍ and ̍non-eating̍–
āhuravbhakṣaṇaṃ viprā hyaśitaṃ nāśitañca.

After completing his midday-rites Durvās came back and realised that Amvarīṣ has kept his vrata by drinking some water. He was infuriated. Amvarīṣa asked for his forgiveness, but Durvāsā̍s anger was not calmed. he created a Kṛtyā– a kind of destructive demi-god from his matted locks. That Kṛtyārushed to Amvarīṣa, with sword in hand, in order to kill him. But Amvarīṣa did not move from his place. The Sudarśana cakra, present there for his protection, burned the Kṛtyā down, and then chased Durvāsā. Seeing the Kṛtyā destroyed and the Sudarśna cakra chasing behind himself, Durvāsā started running. Wherever he went, the Kṛtyā chased behind. Durvāsā found none to give him protection. He went to Brahmā to save his life. But Brahmā expressed his inability to do so. Who would protect one who has behaved so hostile to a distinguished devotee of Viṣṇu? One by one, Durvāsā went to Vyāsa, Kapila, Sanatkumāra and even to God Śiva, but none could assure him. Finally he appealed to God Viṣṇu. Viṣṇu said, “I am bound to my devotees, they are dear to me, and where my devotees are concerned, even my own divine power does not work. Go and ask forgiveness from Amvarīṣa.”

Helpless, Durvāsā came back to Amvarīṣa and fell at his feet. Amvarīṣa was much embarrassed and appealed to the Sudarśana cakra to save the life of Durvāsā. Astonished, Durvāsā said, “I have wronged you. Still you are thinking of my well-being, now I realise the greatness of a true devotee of God.” Out of danger by the kindness of Amvarīṣa, Durvāsā took his meal at his house, and Amvarīṣa ate after that. In bhāgavatapurāṇa, Amvarīṣa is chiefly known as a gentle person and a great devotee of God.

When sage Viśvāmitra was practicing hard asceticism in Puṣkara-tīrtha, Amvarīṣa, the king of Ayodhyā, started a great yajña. Out of jealousy, Indra abducted the yajña-horse. The the priest said to the king, “It is for some offense on your part that the horse has been missing. Now if the yajñ has to be continued, you have to bring a human being in place of that horse.” Amvarīṣa travelled across several countries, in search of a human being who coukd be purchased in exchange for thousands of cows. Finally he came to Bhṛgutuṅga mountain and found sage Ṛcīka, son of Bhṛgu, living there with his family and sons. The kind humbly asked the sage, if he could give away one of his sons in exchange for hundreds and thousands of cows. But Ṛcīka, out of his affection for the eldest son, was not willing to let him go. On the other hand, Ṛcīka̍s wife would not part with her youngest son Śunaka. So the middle son Śunaḥśepha was left out, and he himself submitted to become the sacrificial animal. Amvarīṣa gave a lot of riches and one million of cows to Ṛcīka, and taking Śunaḥsepha along with himself, set out for the yajña-place.

On the way, Amvarīṣa and Śunaḥśepha stopped at Puṣkara-tīrtha for midday bath and meal. While resting there, Śunaḥśepha found his maternal uncle Viśvāmitra, and rushed to his lap, saying, “I have no parents, please save me. I wish that king Amvarīṣa attains a long life and great glory, and I also wish to attain the heavenly abode by tapasyā.” Hearing his appeal, Viśvāmitra comforted him, and asked his sons, if anyone of them could sacrifice himself to save Śunaḥśepha. But nobody was willing, and so Viśvāmitra cursed them. Then he said to Śunaḥśepha, “You accept the thought of becoming the sacrificial animal at the yajña of Amvarīṣa. When they will take you, dressed in red, with a red flower-garland around your neck, with red sandalwwood paste upon your forhead– to be sacrificed as an animal, sing hymns in praise of God Viṣṇu, through the god of fire. In this way you will achieve siddhi.”
vaiṣnavaṃ yūpamāsādya vāgbhiragnimudāhara.

Hearing this, Śunaḥśepha asked Amvarīṣa to hurry to the place of yajña. There, tied to the sacrificial wood, he was brought in the manner as previously said, and he sang paises to Indra and Viṣṇu, as the younger brother of Viṣṇu. Please with the hymns, Indra granted long life to Śunaḥsepha and Amvarīṣa also achieved the fruit of his yajña, more than he expected.

Kṣatriya(s) who do not show their back to the battlefield– attain the absolute fruit of divine bliss in heaven. This is said in the context of Indra-Amvarīṣa discourse in Mahābhārata. Amvarīṣa Nābhāgi, after his death, on his way to the heaven, found that his army-general Sudeva was going far above him, riding on a divine airplane. Sadly, Amvarīṣa asked Indra, “I have performed a disciplined brahmacarya and the conducts as per my guru̍s command, studies Veda(s), served the guests and done my duties to my father̍s clan. I have also performed my duties as a Kṣatriya and conquered the enemies. But this Sudeva was an ordinary soldier of mine, later he became a general and died. How has that Sudeva achieved such a glorified status than myself? He has not performed great yajña(s), not given honorarium to the yājñika brāhmaṇa(s), so how has he attained this status of glory.”

Indra said, “During your reign, the three sons of the rākṣasa-king Śataśṛṅga– Saṃyama, Viyama and Suyama attacked your kingdom with a great multitide of rākṣasa-army, and they caused problem in your yajña, captured all your sons, too. At that time, under the influence of some jealous ministers, you had suspended Sudeva from all important works. But hearing the soldier̍s cry of despair, you called him once again, and sent him to the battle. You also said to the general that you didn̍t wish to see him again until the rākṣasa-army could be defeated and your sons were released of their bondage.

Sudeva set out for the battle and reached the place, where the sons of Amvarīṣ were held in captivity. But the army of the rākṣsa(s) was so large, that Sudeva was concerned– how he could be able to win the battle with such a small number of soldiers with him. So he sent all his soldiers back to Amvarīṣa and himself posed in supplication to Mahādeva.

He uttered the praise of Mahādeva, expressed his purpose, and was about to cut his own head off, in supreme suplication. Mahādeva stopped him, taking his hand, and asked about the matter.

Knowing everything, Mahādeva granted him several weapons, along with his Pāśupata astra and also gave him a chariot as a gift. Armed thus, Sudeva went to fight against the rākṣasa(s). He became victorious and released the princes, but his final battle took place with the demon called Viyama. Sudeva killed him, but heavily wounded by him in a duel, himself breathed his last as well.

After this, Indra gave an elaborate description of how battle can become a yajña, and made the king understand that what his general Sudeva performed was a yuddha-yajña (war as a sacrificial ceremony). Sudeva gave his life away in a face-to-face battle, and so he attained the heavenly abode, and there his position was above than that of his master. The equipments of yajña are compared to the equipments of a battle.

In ancient times, sages present in Prabhāsatīrtha decided that they will travel across all the pilgrimage sites of India. Along with some other famous kings, Amvarīṣa was also accompanying them. Once. coming to Brahma sarovara, sages got down to take a bath and picked up the lotus-stalks. Sage Agastya collected a lotus from this lake, but Indra, king of gods, stole it. Agastya could not understand that, and suspected his fellow-sages. The other sages, and kings who were accompanying them, started uttering curses at the unknown, invisible thief. Amvarīṣa said, “The one who has stolen your lotus– let there be no kindness in him, let him be more ruthless against women, relatives and cows.

From this kind of a curse, coming out of a wounded feeling, it becomes clear that Amvarīṣa himself was a kind-hearted person, and his generosity towards women, relatives and cows was beyond question, and he was naturally inclined to give away cows as donations to brāhmaṇa(s).

Not only the donation of cows, it is said that– king Amvarīṣa gave away the entire earthly realm to the brāhmaṇa(s) and attained the hevenly abode– pradāya sakalaṃ rāṣṭraṃ surālokamavāptavān.

Before his death, Amvarīṣa gathered all his experiences and understanding in life, and said– I have conquered all the vices except one, and that is greed. It is for this greed, that human beings cannot achieve the ability to renounce, and spiritually go down everyday. Greed gives birth to thirst, and from thirst, arises concerns. Out of these concerns, human beings are oriented to such rājasika attributes as Kāma and Krodha, and then they achieve only Tāmasika attibutes. Amvarīṣa wanted to say that– a king who rules the kingdom, assuming the role of a benefactor of his subjects, should conquer this greed; in fact the kingdom of the mind is the true kingdom, and the Ātman is the sole king of this realm–
etadrājyaṃ nānyadastīha rājyam
ātmaiva rājā vidito yathāvat.

With great humility Amvarīṣa said that he could not conquer greed, but he had in fact conquered greed, and taught this lesson. He was such a great warrior and a benevolent king, that taking his name in the morning and night yields fruits of virtue and righteousness, as said in Mahābhārata.