Aśmasārī (Asmasari) is the mantrī (mantri; minister, consultant) of King Śāntanu (Santanu), belonging to Puruvaṁśa(Puruvamsa; the royal dynasty of Puru).In the southern recension of Viṣṇupurāṇa (Vishnupurana), however, the name is given as Aśmarāvin (Asmaravin). Śāntanu was the youngest among the three sons of Pratīpa (Pratipa). Since his elder brother Devāpi (Devapi)went away to live in forest, he accepted the throne. After this , the kingdom suffered from a long-lasting scarcity of rainfall. Scholars said that , Sāntanu has occupied the kingdom, depriving his brother, and so this calamity has come upon his kingdom. Thinking of the benefit of the people, Śāntanu decided to return the kingdom to his brother. Hearing this, his loyal minister Aśmasārī, well-versed in political strategies, secretly sent a person of anti-Vedic opinions, to visit Devāpi. Devāpi got much influenced by the opinions of this person.
Now Śāntanu himself came to his brother and requested him take his kingdom back. The Brāhmaṇas (Brahmanas) present there also put up scriptural arguments, validating the eldest son’s claim to kingdom, trying to convince Devāpi to assume the responsibility of kingship. But Devāpi did not listen to any argument; due to the tactful movement of Aśmasārī, his mind had already turned against the Vedic injunctions and scriptural laws. Finally, the Brāhmaṇas became disgusted with Devāpi. Śāntanu remained the king of Hastināpura (Hastinapura). Since Devāpi opposed the Veda(s), Śāntanu’s claim upon the kingdom was validated in turn. And by the grace of gods, the calamity was also redressed. So it appears that the legend of Aśmasārī actually legitimises Śāntanu’s claim over the kingdom, though he was the youngest.