Shri Indra was the favourite national god of the Vedic Indians, with about 250 hymns dedicated to him in the Rigveda, more than those devoted to any other god and almost one fourth of the total number of hymns of the Rigveda.
Shri Indra is the god of thunder, he is described in the Rigveda as red- or tawny-beared, though the extant sculpture and carvings seem to invariably show him as beardless. His characteristic weapon is the cudgel vajra (`thunder-bolt`). Shri Indra is the pre-eminent drinker of the divine soma (the madhu or `mead` of the gods), the imbibing of which exhilerates him and aids him in his heroic actions.
Shri Indra`s most important deed is the slaying of the asura (`demon`) Vritra, who was a Dragon (ahi). Vritra hoarded and enclosed the vital elements of the universe: waters, light, cows, and Shri Indra struggled in order to free these life-sustaining treasures from the grasp of the dragon Vritra (whose very name, vrtra, means `the Encloser, the Obstructer`) and release them into the world. And he must continually struggle against this Dragon (ahi), who represents the forces of Chaos and Non-Existence (asat).This is why one of Shri Indra`s epithets is vrtrahan `slayer of Vritra, overcomer of resistance`. By defeating these forces he separated and supported heaven and earth.
In his battle with Vritra and other demons, such as Namuci his especial friend was Shri Vishnu, who was often described as helping Indra to defeat Vritra. Vishnu`s function in the battle with Vritra seemed to be primarily to `make space` by means of his famous three strides, for Indra, about to slay Vritra, said to Vishnu: `O my friend Vishnu, stride out widely`. The association of Arjuna (son of Indra) and Shri Krishna (avatara of Vishnu), especially in their companionship during the Mahabharata battle, is thus prefigured by this association of Shri Indra and Vishnu.
By worship and sacrifice (especially soma-sacrifice, as soma-drinking increases Indra`s strength and vigour), humans on earth have helped (and can help) Shri Indra in his struggles, e.g.:
`Sacrifice, Indra, made you grow so mighty, the dear oblation with the pressed soma.
O Worshipful, with sacrifice help our sacrifice, for sacrifice helped your vajra when slaying the dragon`.