The metamorphosis of the meaning of the word ‘asura,’ from ‘beneficent god’ to ‘malevolent spirit or being’ in the Vedic and post-Vedic literature is rather baffling. In early Vedic literature (vide Ṛgveda 1.35.7; 1.131.1) the term denotes the Supreme Spirit. Derived probably from the root ‘as’ (‘to exist’), or ‘asu’ (‘prāṇa or life-force’), it must have originally meant the ‘Self-existent Being’ or the ‘Being of life-force and power.’ It is in this sense that the well-known Vedic deities Indra and Varuṇa have been called ‘asuras’ (ibid 1.54.3; 1.24.14).
But soon the connotation changed. The Nirukta, the standard dictionary of Vedic terms, defines the ‘asuras’ as those ‘who are not satisfied in their positions,’ ‘the ever-fickle’ and ‘those who are deprived of their positions by the suras or devas.’ In later literature, mostly the epics and the purāṇas, they are posited as ‘a-suras’ or ‘anti-gods,’ malevolent beings, ever opposed to the ‘suras’ or ‘devas,’ the ‘beings of goodness and light’. In this sense they are pictured as highly ambitious and aggressive people, rich, civilized and powerful, but ever bent on conquest and self-aggrandizement. And precisely because of this trait of theirs, they are ever in conflict with the devas representing the forces of goodness, refine-ment and culture.
Though conflicts between the devas and the asuras are legion, there have also been occasions when they have cooperated, as for instance, in the case of churning of the ocean to get amṛta or nectar. There have been great asura kings like Prahlāda, Bali, Śambara and Bāṇa who were devotees of God (Viṣṇu or Śiva).
In the mythological lore, the devas and the asuras are depicted as the children of the same father, the sage Kaśyapa, from his two wives Aditi and Diti. Sometimes, the asuras have been described as having been born out of the body of Brahmā or Prajāpati, the Creator.
Whatever be the manner of their origin, the devas and the asuras appear more to be the archetypes of the good and the not-so-good beings in creation.
In the earlier religious literature, the daityas and the dānavas, positively more malevolent beings, had been placed below the asuras. But gradually, the asuras were degraded and identified completely with the former.
One of the very special powers the asuras seemed to possess and excel in, was sorcery and magic.
Some Western scholars of Indology hazard the guess that the asuras were the hostile native rulers and tribes who were opposed to the Āryans. Due to lack of conclusive evidence to clinch the issue, it is difficult to accept such theories. The word may be more etymological and symbolical than historical, racial or social. It is significant to note that Śaṅkara (8th cent. A. D.) the great philosopher mystic, defines the asuras as ‘those addicted to selfish bodily pleasures’ (vide Bṛhadāraṇyaka Upaniṣad. 1.3.1)