In The Rig Veda
The Rig-Veda states,
He under whose supreme control are horses, all chariots, the villages, and cattle;
He who gave being to the Sun and Morning, who leads the waters, He, O men, is Indra. (2.12.7, trans. Griffith)
It further states,
Indra, you lifted up the outcast who was oppressed, you glorified the blind and the lame. (Rg-Veda 2:13:12)
Indra is, with Varuna and Mitra, one of the Ādityas, the chief gods of the Rigveda (besides Agni and the others such as the Ashvins). He delights in drinking Soma, and the central Vedic myth is his heroic defeat of Vṛtrá, liberating the rivers, or alternatively, his smashing of the Vala cave, a stone enclosure where the Panis had imprisoned the cows that are habitually identified with Ushas, the dawn(s). He is the god of war, smashing the stone fortresses of the Dasyu, but he is also is invoked by combatants on both sides in the Battle of the Ten Kings.
The Rig-Veda frequently refers to him as Śakra: the mighty-one. In the Vedic period, the number of gods was assumed to be thirty-three and Indra was their lord. (Some early post Rigvedic texts such as the Khilas and the late Vedic Brihad-Aranyaka Upanishad enumerates the gods as the eight Vasus, the eleven Rudras, the twelve Adityas, Indra, and Prajapati). As lord of the Vasus, Indra was also referred to as Vāsava.
By the age of the Vedanta, Indra became the prototype for all lords and thus a king could be called Mānavendra (Indra or lord of men) and Rama, the hero of the Ramayana, was referred to as Rāghavendra (Indra of the clan of Raghu). Hence the original Indra was also referred to as Devendra (Indra of the Devas). However, Sakra and Vasava were used exclusively for the original Indra. Though modern texts usually adhere to the name Indra, the traditional Hindu texts (the Vedas, epics and Puranas) use Indra, Sakra and Vasava interchangeably and with the same frequency.
"Of the Vedas I am the Sama Veda; of the demigods I am Indra, the king of heaven; of the senses I am the mind; and in living beings I am the living force ." (Bhagavad Gita 10.22)
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